Ink for ink jet printing and method for preparing metal nanoparticles used therein

Abstract

Disclosed is ink for ink jet printing, which comprises: metal nanoparticles comprising a surfactant attached to surfaces thereof; and a first solvent, wherein the metal nanoparticles are present in an amount of 50˜70 parts by weight based on 100 parts by weight of the ink, and the surfactant is present in an amount of 0.5˜5 parts by weight based on 100 parts by weight of the metal nanoparticles. Metal nanoparticles used in the ink and a method for preparing the metal nanoparticles are also disclosed. The method for preparing metal nanoparticles for use in ink for ink jet printing comprises a step of washing surplus surfactant with at least one solvent. By doing so, the surplus surfactant remaining on the surfaces of the metal nanoparticles can be minimized, resulting in a drop in viscosity of ink comprising the metal nanoparticles. Therefore, even if the ink has a metal nanoparticle content of 50 wt % or more, the ink can satisfy a viscosity condition required for ink jet printing, and thus can form an electrode pattern with high conductivity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a graph that shows the results of TGA (Thermogavimetric Analysis) of the ink for ink jet printing according to Example 1;

FIG. 2 is a photographic view taken by SEM (Scanning Electron Microscopy), which shows the ink for ink jet printing according to Example 1 after sintering it;

FIG. 3 1 is a graph that shows the results of TGA (Thermogravimetric Analysis) of the ink for ink jet printing according to Comparative Example 1; and

FIG. 4 is a photographic view taken by SEM (Scanning Electron Microscopy), which shows the ink for ink jet printing according to Comparative Example 1 after sintering it.

MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of the present invention. However, the following examples and comparative examples are illustrative only, and the scope of the present invention is not limited thereto.

EXAMPLE 1

A solution of AgNO₃ in ethylene glycol and a solution of PVP (polyvinyl pyrrolidone), a surfactant, in ethylene glycol were provided, and both solutions were mixed and agitated under reflux for about 1 hour at 150° C. to allow them to react. After the reaction, a dispersion containing Ag nanoparticles with a size of 70˜150 nm dispersed therein was obtained.

To 10 ml of the solution of Ag nanoparticles obtained by the above-described polyol process, 20 ml of acetone and 10 ml of THF were added. The resultant mixture was subjected to centrifugal separation (5000 rpm, 20 minutes) and the supernatant was removed. Next, the precipitate was dispersed again into 5 ml of ethanol. Then, 10 ml of acetone and 10 ml of THF were added thereto, and the resultant mixture was subjected to centrifugal separation, followed by removing the supernatant. The above procedure was repeated twice, and then the resultant precipitate was dispersed into a solvent (such as ethanol) to provide ink.

The ink had a solid content of 52.58 wt % and a viscosity of 14.5 cps. After measuring by TGA, the amount of the remaining surfactant was 1.5 parts by weight based on 100 parts by weight of Ag solid particles (see FIG. 1. The values shown in FIG. 1 are based on the total weight of the ink whose Ag solid content is 52.58 wt %). Additionally, the ink was subjected to ink jetting five times so that it was applied onto a substrate, and the ink was sintered at 580° C. for 30 minutes. After the sintering, a pattern having a line width of 117 μm, a thickness of 3.474 μm and a line length of 4.3 cm was obtained, and the pattern showed a line resistance of 2.698Ω and a specific resistivity of 2.550 μΩ.cm. FIG. 2 was a photograph of the pattern taken by SEM after the sintering. As can be seen from FIG. 2, Ag particles are interconnected with each other to provide excellent conductivity.

EXAMPLE 2

Ag nanoparticles were prepared in the same manner as described in Example 1. Next, ink was provided in the same manner as described in Example 1, except that the ink had a solid content of 70 wt %, and then the ink was subjected to an ink jet patterning test.

The ink had a viscosity of 30.5 cps. The ink was applied onto a substrate by subjecting it to ink jetting once and was sintered at 400° C. for 30 minutes. After the sintering, a pattern having a line width of 90 μm, a thickness of 0.68 μm and a line length of 2.1 cm was obtained, and the pattern showed a line resistance of 16.3Ω and a specific resistivity of 4.75 μΩ.cm. Further, the ink was applied onto a substrate by subjecting it to ink jetting once and was sintered at 580° C. for 30 minutes. After the sintering, a pattern having a line width of 44.7 μm, a thickness of 1.2 μm and a line length of 1.5 cm was obtained, and the pattern showed a line resistance of 12Ω and a specific resistivity of 4.29 μΩ.cm.

COMPARATIVE EXAMPLE 1

Nanoparticles, ink and an electrode pattern were obtained in the same manner as described in Example 1, except that surplus surfactant remaining in the solution of Ag nanoparticles was not sufficiently washed off.

Since the solution had a high viscosity due to the absence of a step of washing the surplus surfactant, the solid content was reduced to ensure an adequate viscosity. for ink jetting. Finally, the solution had a solid content of 21.85 wt % and a viscosity of 16.5 cps. After measuring by TGA, the amount of the surfactant remaining in the solution was 45.0 parts by weight based on 100 parts by weight of the Ag solid particles (see FIG. 3).

After sintering, the resultant pattern had a line width of 134 μm, a thickness of 2.297 μm and a line length of 4.3 cm, and its resistance was not available. FIG. 4 is a photograph of the pattern taken by SEM after the sintering. As can be seen from FIG. 4, Ag particles are not interconnected with each other but are separated from each other, thereby making it difficult to allow electrical conduction.

COMPARATIVE EXAMPLE 2

Ink was provided in the same manner as described in Comparative Example 1, except that the ink had a solid content increased to 50 wt %. In this example, the ink had a viscosity of 100 cPs or higher, which could not be measured by using a viscosimeter provided by the inventors of the present invention. Due to such a high viscosity, ink jetting was not allowed either.

INDUSTRIAL APPLICABILITY

As can be seen from the foregoing, the method for preparing metal nanoparticles for use in ink for ink jet printing comprises a step of washing surplus surfactant with at least one solvent. By doing so, the surplus surfactant remaining on the surfaces of the metal nanoparticles can be minimized, resulting in a drop in viscosity of ink comprising the metal nanoparticles. Therefore, even if the ink has a metal nanoparticle content of 50 wt % or more, the ink can satisfy a viscosity condition required for ink jet printing, and thus can form an electrode pattern with high conductivity.

While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment and the drawings. On the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims.

Claims

1. Ink for ink jet printing, which comprises: metal nanoparticles comprising a surfactant attached to surfaces thereof; anda first solvent,wherein the metal nanoparticles are present in an amount of 50˜70 parts by weight based on 100 parts by weight of the ink, and the surfactant is present in an amount of 0.5□5 parts by weight based on 100 parts by weight of the metal nanoparticles.

2. The ink according to claim 1, which has a viscosity of 1˜50 cPs.

3. The ink according to claim 1, wherein the surfactant is one used for preparing the metal nanoparticles.

4. The ink according to claim 1, wherein the amount of the surfactant can be expressed by a weight loss in a region ranging from complete evaporation temperature of the first solvent to 500° C. as measured by TGA (Thermogravimetric Analysis).

5. The ink according to claim 4, wherein the complete evaporation temperature of the first solvent ranges from 100° C. to 200° C.

6. The ink according to claim 1, which comprises surplus surfactant, not attached to the surfaces of the metal nanoparticles, in an amount of 0.5 parts by weight or less based on 100 parts by weight of the metal nanoparticles.

7. The ink according to claim 1, wherein the metal nanoparticles are at least one type of particle selected from the group consisting of Ag, Cu, Au, Cr, Al, W, Zn, Ni, Fe, Pt and Pb.

8. The ink according to claim 1, wherein the surfactant is a polymeric substance selected from the group consisting of polyvinyl pyrrolidone (PVP), polyethylene imine (PEI), polymethyl vinyl ether (PMVE), polyvinyl alcohol (PVA), polyoxyethylene alkyl phenyl ether and polyethylene sorbitan monostearate.

9. The ink according to claim 1, which is obtained by a method comprising a step of washing surplus surfactant, other than such amount of surfactant as may be attached to surfaces of metal nanoparticles to stabilize the metal nanoparticles, with at least one kind of second solvent so as to remove the surplus surfactant.

10. A method for preparing metal nanoparticles for use in ink for ink jet printing, the method comprising the steps of: (a) adding a surfactant to form metal nanoparticles; and(b) washing surplus surfactant, other than such amount of surfactant as may be attached to surfaces of the metal nanoparticles to stabilize the metal nanoparticles, with at least one kind of second solvent so as to remove the surplus surfactant.

11. The method for preparing metal nanoparticles for use in ink for ink jet printing according to claim 10, wherein the amount of the surfactant attached to the surfaces of the metal nanoparticles to stabilize the metal nanoparticles is 0.5˜5 parts by weight based on 100 parts by weight of the metal nanoparticles.

12. The method for preparing metal nanoparticles for use in ink for ink jet printing according to claim 10, wherein the surplus surfactant, other than such amount of surfactant as may be attached to the surfaces of the metal nanoparticles to stabilize the metal nanoparticles, is present in an amount of 0.5 parts by weight or less based on 100 parts by weight of the metal nanoparticles, after the washing step.

13. The method for preparing metal nanoparticles for use in ink for ink jet printing according to claim 10, wherein the second solvent is capable of dissolving the surfactant.

14. The method for preparing metal nanoparticles for use in ink for ink jet printing according to claim 10, wherein the second solvent is selected from the group consisting of water, methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, DMSO (dimethyl sulfoxide), DMF (N,N-dimethylformamide), N-methylpyrrolidone, acetone, acetonitrile, THF (tetrahydro furan), decane, nonane, octane, heptane, hexane and pentane.

15. The method for preparing metal nanoparticles for use in ink for ink jet printing according to claim 10, wherein the second solvent is added in an amount corresponding to 5˜20 times of the total weight of the surfactant.

16. The method for preparing metal nanoparticles for use in ink for ink jet printing according to claim 10, wherein step (a) is performed by adding a polyol functioning as a reducing agent to a solution containing a metal salt, a surfactant and a third solvent, so as to form metal nanoparticles comprising the surfactant attached to surfaces thereof.

17. Metal nanoparticles for use in ink for ink jet printing, which comprise a surfactant attached to surfaces thereof, in an amount of 0.5˜5 parts by weight based on 100 parts by weight of the metal nanoparticles, wherein the amount of the surfactant is expressed by a weight loss in a region ranging from 100° C. to 500° C. as measured by TGA (Thermogravimetric Analysis).

18. The metal nanoparticles for use in ink for ink jet printing according to claim 17, which are at least one type of particle selected from the group consisting of Ag, Cu, Au, Cr, Al, W, Zn, Ni, Fe, Pt and Pb.