KR20150103857A - Method for preparing conductive ink and conductive ink prepared by the same - Google Patents

Abstract

Provided is a manufacturing method of a conductive ink, as a manufacturing method of a conductive ink, which comprises the steps of: manufacturing a silver nanoparticle capped with oleylamine (OA); and immersing the silver nanoparticle in acetic acid. The present invention can induce ligand substitution and manufacture a conductive ink having excellent conductivity by immersing the conductive metal nanoparticle capped OA with a ligand in acetic acid. A conductive film can be manufactured with a process at low temperatures below 200 degrees Celsius.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive ink,

The present invention relates to a conductive ink manufacturing method and a conductive ink prepared thereby, and more particularly, to a conductive ink prepared by immersing conductive metal nanoparticles in which OA is capped with a ligand into acetic acid to induce ligand replacement and ligand exchange, Conductive ink, and a conductive film can be produced even at a low-temperature process of less than 200 degrees Celsius, and a conductive ink produced thereby.

Traditionally, vacuum deposition and photolithography have the problems of multi-step process and high temperature, high cost and harmful byproduct generation. The printing process is attracting attention as a technique capable of overcoming the limitations of the conventional patterning process due to a fast and simple process, low cost, and low process temperature. The current market for printing electronic devices includes organic photovoltaic devices, flexible batteries, optoelectronic devices, flexible displays, thin film transistors, sensor arrays, and RFID tags. These devices require electrical contacts and conductive structures, and metals with good conductivity are predominantly used. Although several other candidates have been studied as conductive materials, such as conductive polymers, dissolved metals, metal nanoparticles, etc., metals made of metal nanoparticles (NP) and suitable solvents can be used at room temperature, There is an advantage of excellent current conductivity. However, there is a problem that a curing (curing) process at 250 DEG C, which is not suitable for a plastic material having a low glass transition temperature such as polyethylene terephthalate or polycarbonate, must be performed. Therefore, in order to apply a printing process to a plastic substrate, it is necessary to develop a high conductivity ink which can be processed at a low temperature.

The capping ligand treatment process is considered to be quite advantageous in ink manufacture since the capping ligand can completely cover the nanoparticles during chemical synthesis. Addition of surplus ligands to the nanoparticle solution has the effect of controlling the surface properties of the nanoparticles and replacing the original ligands from the surface of the nanoparticles. Particularly, new ligand exchange reaction of new metal nanoparticles through the self-assembly of thiol on new nanoparticles is being studied. Most of the ligands in the conventional studies have carboxylate ions or alcohols as terminals, and adsorption to the surface of nanoparticles proceeds through such terminals to form a stable ligand layer. Such capping ligands are necessary for the chemical synthesis of nanoparticles, but are not required for electrical contact formation or conductive patterns. Under these conditions, substitution of capping ligands has been researched. However, even with low temperature heat treatment, conductive nanoparticles And a method for producing a conductive ink based thereon are not disclosed.

Accordingly, an object of the present invention is to provide a ligand replacement method capable of producing conductive nanoparticles having excellent conductivity even through a new on-heat treatment, and to provide a conductive ink manufacturing method based thereon.

According to an aspect of the present invention, there is provided a conductive ink manufacturing method comprising: preparing silver nanoparticles capped with oleylamine (OA); And a step of immersing the silver nanoparticles in acetic acid.

In one embodiment of the present invention, the step of preparing the oleylamine (OA) -capped silver nanoparticles comprises: adding silver nitrate to oleylamine (OA) and mixing; And heat treating the mixed silver nitrate and the oleylamine (OA).

In one embodiment of the present invention, the acetate ion is bonded to the surface of the silver nanoparticles immersed in the acetic acid, and the removal amount of the oleylamine increases as the immersion time in the immersion step increases.

In one embodiment of the present invention, the acetate ion displaces the oleylamine.

The present invention provides a conductive ink produced by the conductive ink manufacturing method described above.

The present invention also provides a method of manufacturing a conductive ink, comprising the steps of: applying the above-described conductive ink to a substrate surface; And sintering the applied conductive ink. The present invention also provides a method for producing a conductive film.

According to one embodiment of the present invention, the sintering proceeds at a temperature of less than 200 degrees Celsius.

According to an embodiment of the present invention, the substrate is a plastic substrate.

According to one embodiment of the present invention, the conductive ink is agglomerated at a temperature of 150 degrees Celsius or less.

The present invention can produce a conductive ink having excellent conductivity by inducing ligand substitution by immersing conductive metal nanoparticles in which OA is capped with a ligand in acetic acid, and a conductive film can be produced even at a low temperature process of less than 200 degrees Celsius .

Figure 1 shows the TGA results of the ligand-substituted silver nanoparticles after saponification with acetic acid (AA) and the OA-capping silver nanoparticles prepared according to the present invention.
FIG. 2A shows the result of measuring the electrical resistance of the conductive silver ink prepared according to the present invention with respect to the temperature function, and FIGS. 2B to 2D show the results of measuring the electrical resistance of the conductive silver nanoink Of the surface morphology.
Figure 2e is a vertical cross-sectional photograph of a conductive film cured at 100 degrees centigrade for 2 hours.
Fig. 3 shows TEM results of in situ nanoparticles.
FIG. 4A is the FTIR spectrum of the OA-capping nanoparticles and pure OA, FIG. 4B is the FTIR spectrum of the ligand-substituted silver nanoparticles and pure AA prepared according to the present invention.
5A is OA-capping nanoparticles, and 5B is an XPS spectrum of ligand-substituted silver nanoparticles prepared according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings. The following embodiments are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Therefore, the present invention is not limited to the embodiments described below, but may be embodied in other forms. In the drawings, the width, length, thickness, etc. of components may be exaggerated for convenience. Like reference numerals designate like elements throughout the specification.

In order to solve the above problems, the present invention produces silver nanoparticle inks by substituting the ligands of silver nanoparticles by immersing silver nanoparticles coated with OA (oleylamine) in acetic acid. Thus, acetate ions are bound to the silver nanoparticle surface of the conductive ink according to the present invention. Hereinafter, the present invention will be described in more detail by way of examples.

Example

Single phase dispersed silver nanoparticles were prepared. To this end, 2.5 g of silver nitrate (AgNO3) was added to 100 mL of oleylamine (OA, C18H37N) and stirred. Next, OA-capped silver nanoparticles having a diameter of 12.2 nm were synthesized by treating them for 1 hour at 180 ° C for 1 hour (high temperature maturation step) and at 150 ° C for 5 hours (low temperature incubation step). The product was purified through a dispersion-centrifugation process and immersed in a methanol solution to displace excess surface-capping OA.

Next, the nanoparticles were immersed in 99.9% acetic acid at different times to displace OA from the silver nanoparticles. After the acetic acid immersion step, ethanol was added to the suspension and centrifuged at 10,000 rpm for 30 minutes. The resulting nanoparticles were again dispersed in ethanol and then centrifuged. Finally, 30 wt% silver nanoparticles were dispersed in an ethanol-based solvent to prepare a conductive ink.

analysis

Figure 1 shows the TGA results of the ligand-substituted silver nanoparticles and the OA-capped silver nanoparticles, in which OA was replaced with acetate ion after acetic acid (AA) dipping.

Referring to FIG. 1, residual ligand due to increase in acetic acid immersion time can be known. As shown in FIG. 1, the residual ligand was replaced with 4.49 wt% for 1 hour, 4.23 wt% for 2 hours, 3.89 for 3 hours, 3.11 for 5 hours, 2.36 wt% for 10 hours %. Thus, it can be seen that as the silver nanoparticles were immersed in acetic acid, the capping ligand was greatly reduced to about 10 wt% after 10 hours, and even after 1 hour, the ligand was reduced to 8 wt%.

The present invention can be expected to improve the electrical characteristics at low temperature according to the reduction of the ligand described above. For this purpose, 30 wt% silver nanoparticles are prepared as described above. In general, The OA-capping of the nanoparticles was 5.63 μΩcm after sintering at 250 ° C for 20 minutes.

FIG. 2A shows the result of measuring the electrical resistance of the conductive silver ink prepared according to the present invention with respect to the temperature function, and FIGS. 2B to 2D show the results of measuring the electrical resistance of the conductive silver nanoink Of the surface morphology. 2E is a vertical cross-sectional photograph of the conductive film sintered at 100 degrees centigrade for 2 hours.

Referring to FIG. 2A, a similar resistance (7.13 mu OMEGA cm) was found at 250 degrees Celsius in only 5 minutes, and after 10 minutes curing, it was 4.54 mu OMEGA cm. This figure is similar to the resistance of a material in a normal bulk, and is much better than the resistance of an OA-capping ink under the same conditions. In addition, silver nanoparticle inks with reduced ligands according to the present invention have processability at low temperatures. OA-capping, as compared to inks, the ligand-substituted silver nanoparticles prepared according to the present invention exhibit significantly improved electrical properties at 200 degrees Celsius and exhibit improved electrical properties at 100 degrees Celsius and 150 degrees Celsius through 1 hour of curing time The resistance value was less than 10 μΩcm. Thus, temperatures below 200 degrees Celsius, for example, temperatures as low as 100 and 150 degrees Celsius, are temperatures at which a plastic substrate can be used, which means that according to the method according to the invention, the advantages of the ligand-substituted silver nanoparticles to be.

Referring to Figs. 2c to 2d, a well-agglomerated surface morphology of the conductive film of the present invention cured at 100 deg. C for 30 minutes, 1 hour and 2 hours can be confirmed. All resistance values were calculated according to the measured thickness (200 nm 10 nm) and the surface resistance of the conductive film.

As described above, the excellent electrical properties of the conductive ink and the film according to the present invention are attributed to the reduced number of ligands due to acetic acid immersion, which makes it easier to aggregate silver nanoparticles in the ligand reduction and heat treatment process (sintering process) . Further, the acetic acid immersion process induces ligand exchange as well as ligand reduction. According to the acetic acid immersion treatment according to the present invention, OA having a high boiling point (about 350 degrees Celsius) and being thermally stable has a shorter chain And is exchanged with the less stable acetate ion.

Therefore, it can be seen that OA ligand removal on the surface of silver nanoparticles is carried out by acetic acid treatment according to the present invention by ligand replacement (exchange) of silver nanoparticles. In addition, the sintering time and temperature can be reduced by such a ligand substitution, resulting in a possibility of application to a plastic substrate and an effect of improving conductivity.

Fig. 3 shows TEM results of in situ nanoparticles.

Referring to FIG. 3, the TEM images of the OA-capping silver nanoparticles of FIGS. 3 (a) through 3 (f) photographed while increasing the temperature by 25 to 300 degrees are ligand-substituted silver nanoparticles and g-1 are in their original state. According to the present invention, silver nanoparticles reduced in OA ligand according to the present invention exhibit agglutination at a temperature of about 150 ° C or less, precisely about 100 ° C, but the conventional state of OA-capping nanoparticles It can be seen that the flocculation starts at 200 ° C., and the flocculation phenomenon becomes larger as the temperature increases. The above results indicate that when the conductive ink according to the present invention, which is agglomerated at a temperature of 150 DEG C or less, is used, a nanoparticle-based conductive material having excellent conductivity even by a sintering process at a temperature of less than 200 DEG C (for example, ) Can be produced.

FIG. 4A is the FTIR spectrum of the OA-capping nanoparticles and pure OA, FIG. 4B is the FTIR spectrum of the ligand-substituted silver nanoparticles and pure AA prepared according to the present invention.

Referring to FIG. 4A, the spectrum of OA-capping nanoparticles is similar to that of OA. Two sharp peaks appearing at 2921 and 2852 cm < -1 > in the two spectra are attributable to the CH2 stretching modes of asymmetry and symmetry, respectively. The 2642 cm-1 peak is attributed to the C-H stretching mode of the OA carbon chain and the band at 1330-1650 cm-1 is due to the -NH2 bending mode. The surface active ligands in the adsorption state are strongly bound to the surface of the silver nanoparticles, and as a result, the characteristic band shifts to the low frequency region due to the deformation vibration of the primary amine.

On the other hand, the silver nanoparticles immersed in acetic acid for 10 hours according to the present invention do not exhibit peak characteristics corresponding to acetic acid (see FIG. 4B). Strong 1710 cm < -1 > peak from the C = O staining mode did not appear in the silver nanoparticles according to the present invention, and symmetric and asymmetric steric modes of carboxylate ion at 1405 and 1562 cm & In silver nanoparticles.

5A is OA-capping nanoparticles, and 5B is an XPS spectrum of ligand-substituted silver nanoparticles prepared according to the present invention.

Referring to FIG. 5A, two C1s peaks were shown at 284.6 and 286.7 eV. Generally, the 284.6 eV peak overlaps the carbon atoms of the alkane chain, and the 286.7 eV peak overlaps the different inter-element bonds (C-N and C-O). However, referring to FIG. 5B, there is somewhat different result from FIG. 5A. The peaks at 284.6 eV and 286.5 eV are similar to the OA-capping nanoparticles, but the peak at 286.7 eV belongs to the carboxylate carbon. The C1s peak corresponding to the carboxyl group carbon (290.0 eV) did not appear. This surface analysis demonstrates well the exchange of ligands from OA to carboxylate ions. Further, it can be seen that the carboxylate ion is produced from acetic acid which is an immersion solvent.

As discussed above, the present invention induces ligand substitution by immersing the conductive metal nanoparticles in which OA is capped with a ligand in acetic acid, whereby a conductive film can be prepared even by a low-temperature process with improved conductivity.

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Accordingly, the disclosed embodiments are to be considered in an illustrative rather than a restrictive sense, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

Claims (10)

As a method for producing a conductive ink,
Preparing silver nanoparticles capped with oleylamine (OA); And
Wherein the silver nanoparticles are immersed in acetic acid. The method according to claim 1,
The step of preparing the silver nanoparticles capped with oleylamine (OA)
Adding silver nitrate to oleylamine (OA) and mixing; And
And heat treating the mixed silver nitrate and the oleylamine (OA). The method according to claim 1,
And the acetate ion is bound to the surface of the silver nanoparticles immersed in the acetic acid. The method according to claim 1,
Wherein the removal amount of the oleylamine is increased as the immersion time in the immersion step is increased. The method of claim 3,
Wherein the acetate ion substitutes for the oleylamine. A conductive ink produced by the method for producing a conductive ink according to any one of claims 1 to 5. Applying a conductive ink according to claim 6 to a substrate surface; And
And sintering the applied conductive ink. ≪ RTI ID = 0.0 > 11. < / RTI > 8. The method of claim 7,
Wherein the sintering is performed at a temperature of less than 200 degrees Celsius. 8. The method of claim 7,
Wherein the substrate is a plastic substrate. 8. The method of claim 7,
Wherein the conductive ink is agglomerated at a temperature of 150 DEG C or less.

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