WO2025136082A1

WO2025136082A1 - Conductive nanoparticle formulation

Info

Publication number: WO2025136082A1
Application number: PCT/MY2024/050096
Authority: WO
Inventors: Aiman Sajidah ABD AZIZ; Siti Zuulaika REJAL; Syed Muhammad Hafiz SYED MOHD JAAFAR; Nora'zah Abdul Rashid; Suraya Sulaiman
Original assignee: Mimos Bhd
Current assignee: Mimos Bhd
Priority date: 2023-12-21
Filing date: 2024-12-12
Publication date: 2025-06-26
Anticipated expiration: 2026-06-21

Abstract

A conductive nanoparticle formulation and method of preparing the conductive nanoparticle formulation, wherein the conductive nanoparticle formulation comprising silver precursor, reducing agent, stabilizer, encapsulating agent, UV monomer resin and solvent and wherein the encapsulating agent comprises primary encapsulating agent and secondary encapsulating agent.

Description

CONDUCTIVE NANOPARTICLE FORMULATION

FIELD OF THE INVENTION

The present invention relates to a conductive nanoparticle formulation and method of manufacturing thereof, in particular the conductive nanoparticle formulation is incorporated into an ink formulation which is subsequently printed on a polymer substrate using an inkjet printer and cured using ultraviolet radiation to prepare a printed electronic.

BACKGROUND OF THE INVENTION

In recent times, inkjet printing has been widely used in various industries such as production of printed electronics. Generally, silver (Ag) inks are used for inkjet printing of printed electronics due to its high electrical conductivity. Typically, high temperatures ranging between 100^sC to 200^sC are required for sintering the printed silver inks on the surface of a polymer substrate to enhance the conductivity of the silver ink as well as improve its adhesion on the polymer substrate.

However, sintering of silver inks at high temperature on temperature sensitive polymer substrate such as but not limited to polyethylene terephthalate (PET) can cause deformation and warping of the polymer substrate which subsequently results in delamination and peeling of the printed silver ink from the polymer substrate. Further, the inadequate adhesion between the silver ink and polymer substrate can result in electrical discontinuities and/or irregularities in the conductive patterns.

In addition, ink formulations that are cured at high temperature have low compatibility with smooth or non-porous surfaces. Hence, this limitation compromises the adhesion of the ink formulation on the substrate which results in printed electronics with poor quality.

Further, high amounts of volatile organic compounds (VOCs) are generally incorporated into silver ink formulations to accelerate the long curing time which subsequently improves the manufacturing efficiency. However, the use of VOCs is hazardous and poses environmental risks, as VOCs can easily evaporate into the atmosphere, subsequently compromising air quality. This can lead to health issues for both humans and wildlife, including but not limited to respiratory problems and eye irritation. Furthermore, the high volatility of VOCs can also lead to the drying up of ink within the inkjet nozzle, resulting in blockages in the printing process.

Furthermore, printed electronics produced using silver inks exhibit lower resistance to fading and scratching as highly prone to chemical degradation over time. These factors can shorten the lifespan of printed electronics which subsequently requires more frequent replacements or repairs.

Having said the above, an approach is required to identify an ink formulation that can overcome the abovementioned shortcomings in which the ink formulation exhibits desired adhesion on the polymer substrate while the resultant printed electronic exhibit improved conductivity and durability.

SUMMARY OF THE INVENTION

The present invention relates to a conductive nanoparticle formulation comprising silver precursor, wherein the silver precursor is used in an amount ranging between 5% to 50% by weight of the conductive nanoparticle formulation, reducing agent, wherein the reducing agent is used in an amount ranging between 5% to 50% by weight of the conductive nanoparticle formulation, stabilizer, wherein the stabilizer is used in an amount ranging between 0.3% to 5% by weight of the conductive nanoparticle formulation, encapsulating agent, wherein the encapsulating agent consist of primary encapsulating agent and secondary encapsulating agent, wherein the primary encapsulating agent is used in an amount ranging between 0.3% to 5% by weight of the conductive nanoparticle formulation, wherein the secondary encapsulating agent is used in an amount ranging between 1% to 9% by weight of the conductive nanoparticle formulation, UV monomer resin, wherein the UV monomer resin is used in an amount ranging between 0.1% to 15% by weight of the conductive nanoparticle formulation and solvent, wherein the solvent is used in an amount ranging between 20% to 95% by weight of the conductive nanoparticle formulation.

Also, the present invention relates to a method of preparing conductive nanoparticle formulation, wherein the method comprises the steps of (i) adding primary encapsulating agent and secondary encapsulating agent into stabilizer while stirring to produce a copolymer at a temperature ranging between 25°C to 30°C for a duration ranging between 30 minutes to 1 hour, (ii) adding silver precursor into reducing agent dropwise while stirring to produce a reduced silver colloidal solution at a temperature ranging between 25°C to 30°C until the colour of the reduced silver colloidal solution turn into light yellow, (iii) adding the copolymer obtained from step (i) into the reduced silver colloidal solution obtained from step (ii) while stirring to produce a first mixture at a temperature ranging between 25°C to 30°C for a duration ranging between 8 hours to 10 hours, (iv) adding UV monomer resin into the first mixture obtained from step (iii) while stirring to produce a second mixture at a temperature ranging between 25°C to 120°C for a duration ranging between 2 hours to 10 hours, (v) stirring the second mixture obtained from step (iv) to produce homogenous second mixture at a temperature ranging between 25°C to 30°C for a duration ranging between 12 hours to 24 hours, (vi) ultrasonicating the homogenous second mixture obtained from step (v) to produce a third mixture at temperature ranging between 50^sC to 70^sC for a duration ranging between 40 minutes to 60 minutes, (vii) adding a solvent into the third mixture obtained from step (vi) in a ratio ranging between 1 :9 to 1.8:8.2 while stirring to produce a fourth mixture at a temperature ranging between 25°C to 30°C for a duration ranging between 0.5 hours to 1 hour, (viii) centrifuging the fourth mixture obtained from step (vii) at least once to obtain supernatant at a temperature ranging between 25°C to 30°C for a duration ranging between 10 minutes to 20 minutes, (ix) adding a solvent into the supernatant obtained from step (viii) in a ratio ranging between 1 :9 to 3:7 while stirring to produce a fifth mixture at a temperature ranging between 25°C to 30°C for a duration ranging between 5 minutes to 30 minutes and (x) ultrasonicating the fifth mixture obtained from step (ix) to produce conductive nanoparticle formulation at a temperature ranging between 20^sC to 25^SC for a duration ranging between 30 minutes to 90 minutes.

Additional aspects, features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments of the invention. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

The present invention will be fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein:

In the appended drawing:

FIGURE 1 is a flowchart showing the steps involved in preparing the conductive nanoparticle formulation in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Detailed description of preferred embodiments of the present invention is disclosed herein. It should be understood, however, that the embodiments are merely exemplary of the present invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as the basis for the claims and for teaching one skilled in the art of the invention. The numerical data or ranges used in the specification are not to be construed as limiting.

The present invention relates to a conductive nanoparticle formulation and method of manufacturing thereof, in particular the conductive nanoparticle formulation is incorporated into an ink formulation which is subsequently printed on a polymer substrate using an inkjet printer and cured using ultraviolet (UV) radiation to prepare a printed electronic, wherein the ink formulation exhibits desired adhesion on the polymer substrate while the resultant printed electronic exhibit improved conductivity and durability.

First aspect of the present invention discusses on a conductive nanoparticle formulation, wherein the conductive nanoparticle formulation is subsequently incorporated into an ink formulation to produce a printed electronic device using an inkjet printer. The conductive nanoparticle formulation of the present invention has total solid content ranging between 8% to 20% by weight, preferably 10% by weight, viscosity ranging between 2 cP to 15 cP and conductivity ranging between 10⁵ S/m to 10⁷ S/m. The conductive nanoparticle formulation of the present invention is in the form of colloid. The conductive nanoparticle formulation comprises silver precursor, reduce agent, stabilizer, encapsulating agent, UV monomer resin and solvent (composition as described in Table 1 ).

The silver precursor is selected from the group consisting of silver nitrate, silver chloride, silver sulphonate, silver methanesulphonate, silver trifluoromethanesulphonate, silver acetate, silver citrate and mixtures therefrom, preferably silver nitrate. The silver precursor is used in an amount ranging between 5% to 50%, preferably ranging between 8% to 20%, and most preferably 13.4% by weight of the conductive nanoparticle formulation.

The reducing agent is selected from the group consisting of diethanolamine, triethanolamine, ethylene glycol, polyethylene glycol, ascorbic acid, sodium borohydride, sodium citrate, ascorbate and mixtures therefrom, preferably diethanolamine. The reducing agent is used in an amount ranging between 5% to 50%, preferably ranging between 10% to 30%, and most preferably 24.8% by weight of the conductive nanoparticle formulation.

The stabilizer is selected from the group consisting of polyvinyl pyrrolidone, polyvinylidene fluoride, polyvinyl alcohol, polyethylene glycol, citrate, gelatin, chitosan and mixtures therefrom, preferably polyvinyl pyrrolidone. The stabilizer is used in an amount ranging between 0.3% to 5%, preferably ranging between 1% to 3%, and most preferably 1.5% by weight of the conductive nanoparticle formulation.

The encapsulating agent consist of primary encapsulating agent and secondary encapsulating agent. The primary encapsulating agent is polyacrylic acid, wherein the primary encapsulating agent is used in an amount ranging between 0.3% to 5%, preferably ranging between 1% to 3%, and most preferably 1 .5% by weight of the conductive nanoparticle formulation. The secondary encapsulating agent is polyvinylpyrrolidone, wherein the secondary encapsulating agent is used in an amount ranging between 1% to 9%, preferably ranging between 3% to 5%, and most preferably 1.5% by weight of the conductive nanoparticle formulation. The encapsulating agent has a molecular weight ranging between 40000 g/mol to 120000 g/mol. The UV monomer resin is selected from the group consisting of polyethylene glycol) monoacrylate, polyethylene glycol) diacrylate, polyethylene glycol) triacrylate and mixtures therefrom, preferably polyethylene glycol) diacrylate. The UV monomer resin is used in an amount ranging between 0.1% to 15%, preferably ranging between 0.5% to 5%, and most preferably 1.6% by weight of the conductive nanoparticle formulation. The UV monomer resin has a molecular weight ranging between 200 g/mol to 600 g/mol, preferably 575 g/mol.

The solvent is selected from the group consisting of deionized water, ethanol, acetone, isopropyl, dioxane, ethylene glycol, ethylamine, water miscible solvent and mixtures therefrom, preferably deionized water. The solvent is used in an amount ranging between 20% to 95%, preferably ranging between 45% to 60%, and most preferably 57.2% by weight of the conductive nanoparticle formulation.

Table 1 shows the chemical components and compositions thereof (as described above) used to prepare the conductive nanoparticle formulation of the present invention.

Table 1 : Chemical components and compositions thereof used to prepare the conductive nanoparticle formulation of the present invention

Second aspect of the present invention, referring to Figure 1 , discusses on a method of preparing the conductive nanoparticle formulation of the present invention, wherein the conductive nanoparticle formulation of the present invention is prepared using the chemical components and compositions as summarized in Table 1 , wherein the method comprises the steps of: i. adding primary encapsulating agent and secondary encapsulating agent into stabilizer (as described in Table 1 ) while stirring to produce a copolymer, wherein the copolymer is continuously stirred at a speed ranging between 400 rpm to 500 rpm at a temperature ranging between 25°C to 30°C for a duration ranging between 30 minutes to 1 hour; ii. adding silver precursor into reducing agent (as described above and Table 1 ) dropwise while stirring to produce a reduced silver colloidal solution, wherein the reduced silver colloidal solution is continuously stirred at a speed ranging between 400 rpm to 500 rpm at a temperature ranging between 25°C to 30°C until the colour of the reduced silver colloidal solution turn into light yellow; iii. adding the copolymer obtained from step (i) into the reduced silver colloidal solution obtained from step (ii) while stirring to produce a first mixture, wherein the first mixture is continuously stirred at a speed ranging between 50 rpm to 100 rpm at a temperature ranging between 25°C to 30°C for a duration ranging between 8 hours to 10 hours; iv. adding UV monomer resin (as described above and Table 1 ) at a flow rate ranging between 5 ml/min to 20 ml/min into the first mixture obtained from step (iii) while stirring to produce a second mixture, wherein the second mixture is continuously stirred at a speed ranging between 50 rpm to 100 rpm at a temperature ranging between 25°C to 120°C for a duration ranging between 2 hours to 10 hours; v. stirring the second mixture obtained from step (iv) to produce homogenous second mixture, wherein the homogenous second mixture is continuously stirred at a speed ranging between 50 rpm to 100 rpm at a temperature ranging between 25°C to 30°C for a duration ranging between 12 hours to 24 hours, preferably 22.5 hours to allow the silver nanoparticles to aggregate and grow as core nanoparticles in UV monomer resin copolymer shell matrix; vi. ultrasonicating the homogenous second mixture obtained from step (v) to produce a third mixture, wherein the third mixture is sonicated at a frequency ranging between 37 kHz to 80 kHz, amplitude ranging between 80% to 100% and temperature ranging between 50^sC to 70^sC for a duration ranging between 40 minutes to 60 minutes; vii. adding a solvent at a flow rate ranging between 5 ml/min to 15 ml/min into the third mixture obtained from step (vi) in a ratio ranging between 1 :9 to 1 .8:8.2 while stirring to produce a fourth mixture, wherein the fourth mixture is continuously stirred at a speed of 50 rpm to 100 rpm at a temperature ranging between 25°C to 30°C for a duration ranging between 0.5 hours to 1 hour; viii. centrifuging the fourth mixture obtained from step (vii) at least once, preferably thrice to obtain supernatant, wherein the centrifugation is carried out at a speed ranging between 6000 rpm to 12000 rpm at a temperature ranging between 25°C to 30°C for a duration ranging between 10 minutes to 20 minutes; ix. adding a solvent (as described in Table 1 ) at a flow rate ranging between 5 ml/min to 15 ml/min into the supernatant obtained from step (viii) in a ratio ranging between 1 :9 to 3:7 while stirring to produce a fifth mixture, wherein the fifth mixture is continuously stirred at a speed of 5 rpm to 100 rpm at a temperature ranging between 25°C to 30°C for a duration ranging between 5 minutes to 30 minutes; and x. ultrasonicating the fifth mixture obtained from step (ix) to produce conductive nanoparticle formulation of the present invention, wherein the conductive nanoparticle formulation of the present invention is sonicated at a frequency ranging between 37 kHz to 80 kHz, preferably 40 kHz at a temperature ranging between 20^sC to 25^SC, preferably 25 ^SC for a duration ranging between 30 minutes to 60 minutes.

The method as described in the second aspect of the present invention comprises a step (iii) of adding the copolymer obtained from step (i) into the reduced silver colloidal solution, wherein this step (iii) is crucial to grow silver nanoparticle and simultaneously allow the copolymer to encapsulate the silver nanoparticle.

The method as described in the second aspect of the present invention comprises a step (iv) of adding UV monomer resin into the first mixture, wherein the step (iv) is crucial to co-polymerize UV monomer resin with the copolymer which forms an encapsulant matrix (shell) around the silver nanoparticle. This can provide stability and prevent aggregation or settling of the colloidal particles. UV monomer resin also helps to control the arrangement or spacing of the colloidal particles during the polymerization process.

The method as described in the second aspect of the present invention comprises a step (vi) of ultrasonicating the homogenous second mixture to reduce the size of the silver nanoparticle. The ultrasonication process promotes uniform particle size distribution which prevents the formation of larger aggregates particles and ensures a stable suspension.

The method as described in the second aspect of the present invention comprises a step (vii) of adding a solvent into the third mixture, wherein the step (vii) is crucial to remove impurities such as but not limited to unreacted substances and byproducts. The solvent used in the step (vii) is a polar solvent such as but not limited to deionized water, ethanol, isopropanol, acetone and mixtures therefrom.

The method as described in the second aspect of the present invention comprises a step (vii) of centrifuging the fourth mixture to obtain supernatant, wherein the supernatant is the precipitated UV monomer resin copolymer encapsulated silver nanoparticle, wherein the silver nanoparticle core has a particle size ranging between 20 nm to 50 nm and wherein the UV monomer resin copolymer shell has a particle size ranging between 1 nm to 3 nm.

The method as described in the second aspect of the present invention comprises a step (x) of ultrasonicating the fifth mixture, wherein the ultrasonication is conducted for at least one cycle, preferably two cycles, wherein each cycle comprises the steps of: i. mixing the fifth mixture at a speed of 300 rpm at a temperature of 25°C for a duration of 5 minutes; ii. ultrasonicating the fifth mixture at a frequency of 40 kHz at a speed of 300 rpm at a temperature of 25°C for a duration of 30 minutes; iii. mixing the fifth mixture at a speed of 300 rpm at a temperature of 25°C for a duration of 5 minutes; iv. ultrasonicating the fifth mixture at a frequency of 40 kHz at a speed of 300 rpm at a temperature of 25°C for a duration of 30 minutes; and v. mixing the fifth mixture at a speed of 300 rpm at a temperature of 25°C for a duration of 5 minutes.

Third aspect of the present invention discusses on an ink formulation, wherein the ink formulation is used to produce a printed electronic device using an inkjet printer. The ink formulation of the present invention has total solid content ranging between 10 to 15 by weight, viscosity ranging between 1 mPa.s to 10 mPa.s, surface tension ranging between 20 mN/m to 55 mN/m, fluid density ranging between 1 g/cm³ to 5 g/cm³and conductivity ranging between 10⁴S/m to 10⁵S/m.

The ink formulation comprises conductive nanoparticle formulation of the present invention, UV monomer resin, photopolymerization initiator, surfactant, polar organic solvent and polar solvent (composition as described in Table 2).

The conductive nanoparticle formulation of the present invention is summarized in Table 1. The conductive nanoparticle formulation of the present invention is used in an amount ranging between 8% to 20%, preferably ranging between 8% to 15%, and most preferably 10% by weight of the ink formulation.

The UV monomer resin is selected from the group consisting of polyethylene glycol) monoacrylate, polyethylene glycol) diacrylate, polyethylene glycol) triacrylate and mixtures therefrom, preferably poly(ethylene glycol) diacrylate. The UV monomer resin is used in an amount ranging between 3% to 15%, preferably ranging between 5% to 12%, and most preferably 7% by weight of the ink formulation.

The photopolymerization initiator is selected from the group consisting of 2,2- dimethoxy-2-phenylacetophenone (DMPP), 2-hydroxy-4’-(2-hydroxyethoxy)-2- methylpropiophenone, 1 -hydroxycyclohexyl phenyl ketone, benzoin methyl ether (BME0, benzoin ethyl ether (BEE) and mixtures therefrom. The photopolymerization initiator is used in an amount ranging between 0.01% to 3%, preferably ranging between 0.5% to 2%, and most preferably 1 .5% by weight of the ink formulation.

The surfactant is selected from the group consisting of triethanolamine, sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and mixtures therefrom. The surfactant is used in an amount ranging between 0.1% to 3%, preferably ranging between 0.5% to 1%, and most preferably 0.8% by weight of the ink formulation.

The polar organic solvent is selected from the group consisting of methanol, ethanol and mixtures therefrom. The polar organic solvent is used in an amount ranging between 0.1% to 10%, preferably ranging between 0.5% to 2%, and most preferably 0.7% by weight of the ink formulation.

The polar solvent is selected from the group consisting of deionized water, ethanol, methanol and mixtures therefrom. The polar solvent is used in an amount ranging between 50% to 99%, preferably ranging between 70% to 90%, and most preferably 80% by weight of the ink formulation.

Table 2 shows the chemical components and compositions thereof (as described above) used to prepare the ink formulation of the present invention.

Table 2: Chemical components and compositions thereof used to prepare the ink formulation of the present invention

Fourth aspect of the present invention discusses on a method of preparing the ink formulation of the present invention, wherein the ink formulation of the present invention is prepared using the chemical components and compositions as summarized in Table 2, wherein the method comprises the steps of: i. adding UV monomer resin, photopolymerization initiator, surfactant, polar organic solvent and polar solvent one after another with no particular order into conductive nanoparticle formulation of the present invention (as described in Table 2) while stirring to produce a mixture, wherein the mixture is continuously stirred at a speed ranging between 1500 rpm to 2000 rpm at a temperature ranging between 20°C to 25°C for a duration ranging between 1 minute to 5 minutes; ii. stirring the mixture obtained from step (i) to produce homogenous mixture, wherein the homogenous mixture is continuously stirred at a speed ranging between 1500 rpm to 2000 rpm at a temperature ranging between 25°C to 35°C for a duration ranging between 1 minute to 5 minutes; iii. degassing the homogeneous mixture obtained from step (ii) to produce degassed mixture, wherein the degassed mixture is continuously stirred at a speed ranging between 500 rpm to 1000 rpm at a temperature ranging between 25°C to 35°C for a duration ranging between 30 seconds to 60 seconds; and iv. mixing and degassing the degassed mixture obtained from step (iii) to produce ink formulation of the present invention, wherein the ink formulation of the present invention is continuously stirred at a speed ranging between 500 rpm to 1000 rpm at a temperature ranging between 25°C to 35°C for a duration ranging between 30 seconds to 60 seconds.

Fifth aspect of the present invention discusses on a method of printing the ink formulation of the present invention on a substrate using an inkjet printer to produce a printed electronic, wherein the ink formulation of the present invention is filtered using but not limited to disk filter to produce refined ink formulation of the present invention prior to printing on the substrate and wherein the disc of the disc filter has pore size ranging between 0.2 pm to 5 pm, preferably 0.2 pm. The ink formulation of the present invention is printed on the substrate using an inkjet printer having operating temperature up to 100^sC, preferably 30^sC cartridge head and 30^sC to 40^sC substrate stage heating temperature. The ink formulation of the present invention is printed on the substrate using inkjet printer at jetting voltage ranging between 10 to 100 V, frequency ranging between 5 kHz to 100 kHz, drop spacing ranging between 10 pm to 25 pm, pressure ranging between -2 mbar to -18 mbar, cartridge temperature ranging between 25^SC to 35^SC, platen temperature ranging between 30^sC to 40^sC and drop velocity ranging between 5.0 m/sec to 10 m/sec. The substrate can be but not limited to polymeric based substrate, metal foil based substrate, polyester based substrate and mixtures thereof. The polymeric based substrate is selected from the group consisting of polyethylene terephthalate (PET), thermoplastic polyurethane (TPU), polyimide (PI), polyethylene naphthalate (PEN), polyetherether-ketone (PEEK) and mixtures therefrom. The polyester based substrate is selected from the group consisting of paper, cloth, cotton, nylon, silk and mixture therefrom.

The printed ink formulation on the substrate is UV photocured under UV radiation having wavelength ranging between 200 nm to 400 nm at inert gas flow ranging between 2 bar to 5 bar or ambient environment for a duration ranging between 30 seconds to 600 seconds at intensity ranging between 10 mW/cm² to 500 mW/cm². The printed electronic device of the present invention can be but not limited to radio-frequency identification (RFID) tags, printed sensors, flexible and printed circuit board, printed antennas, smart textile for wearable technologies and photovoltaic devices.

The following examples are constructed to illustrate the present invention in a nonlimiting sense.

The printed electronic device of the present invention is prepared using the ink formulation of the present invention as described above and its compositions as summarized in Table 2 based on the method as described in the fourth aspect of the present invention, wherein the ink formulation comprises the conductive nanoparticle formulation of the present invention as summarized in Table 1 which is prepared based on the method as described in the second aspect of the present invention. Test results for the UV cured ink formulation of the present invention

For the purpose of the present invention, Set A represents the conventional silver ink formulation which is non-UV cured on a PET substrate. Set B represents the ink formulation of the present invention which is UV-cured on a PET substrate.

The ink formulations mentioned above are measured for their pencil hardness according to ASTM D3363 Pencil Hardness test, conductivity and adhesion properties.

Table 3 shows the comparison of pencil hardness for conventional ink formulation and formulation of the present invention.

Table 3: Comparison of pencil hardness for conventional ink formulation and ink formulation of the present invention

Based on the results obtained in Table 3, it is noticeable that the ink formulation of the present invention (Set B) has higher pencil hardness as compared to conventional ink formulation (Set A), indicating that the ink formulation of the present invention adhered well to the PET substrate. This proves that the ink formulation of the present invention has high resistance to scratching and improved durability, indicating that the ink formulation of the present invention is suitable for various applications that require resistance to wear and scratching.

Table 4 shows the comparison of conductivity for conventional ink formulation and ink formulation of the present invention. Table 4: Comparison of conductivity for conventional ink formulation and formulation of the present invention

Based on the results obtained in Table 4, it is noticeable that the ink formulation of the present invention (Set B) has higher conductivity as compared to conventional ink formulation (Set A), indicating that the ink formulation of the present invention has improved electrical properties.

Table 5 shows the comparison of work of adhesion (WoA) of conventional ink formulation and formulation of the present invention Table 5: Comparison of work of adhesion (WoA) of conventional ink formulation and formulation of the present invention

Based on the results obtained in Table 5, it is noticeable that the ink formulation of the present invention (Set B) has higher work of adhesion (WoA) as compared to conventional ink formulation (Set A), indicating that the ink formulation of the present invention adhered well on the polyethylene terephthalate, polyimide and polyvinyl alcohol substrates.

As a whole, the ink formulation having conductive nanoparticle of the present invention is able to overcome the conventional shortcomings in which the ink formulation exhibits desired adhesion on the polymer substrate while the resultant printed electronic exhibit improved conductivity and durability.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", “including” and “having” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.

The method, steps, processes and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. The use of the expression “at least” or “at least one” suggests the use of one or more elements, as the use may be in one of the embodiments to achieve one or more of the desired objects or results.

Claims

1 . A conductive nanoparticle formulation comprising:

(a) silver precursor, wherein the silver precursor is used in an amount ranging between 5% to 50% by weight of the conductive nanoparticle formulation;

(b) reducing agent, wherein the reducing agent is used in an amount ranging between 5% to 50% by weight of the conductive nanoparticle formulation;

(c) stabilizer, wherein the stabilizer is used in an amount ranging between 0.3% to 5% by weight of the conductive nanoparticle formulation;

(d) encapsulating agent, wherein the encapsulating agent consist of primary encapsulating agent and secondary encapsulating agent, wherein the primary encapsulating agent is used in an amount ranging between 0.3% to 5% by weight of the conductive nanoparticle formulation and wherein the secondary encapsulating agent is used in an amount ranging between 1% to 9% by weight of the conductive nanoparticle formulation;

(e) UV monomer resin, wherein the UV monomer resin is used in an amount ranging between 0.1% to 15% by weight of the conductive nanoparticle formulation; and

(f) solvent, wherein the solvent is used in an amount ranging between 20% to 95% by weight of the conductive nanoparticle formulation.

2. The conductive nanoparticle formulation as claimed in claim 1 , wherein the silver precursor is selected from the group consisting of silver nitrate, silver chloride, silver sulphonate, silver methanesulphonate, silver trifluoromethanesulphonate, silver acetate, silver citrate and mixtures therefrom.

3. The conductive nanoparticle formulation as claimed in claim 1 , wherein the reducing agent is selected from the group consisting of diethanolamine, triethanolamine, ethylene glycol, polyethylene glycol, ascorbic acid, sodium borohydride, sodium citrate, ascorbate and mixtures therefrom.

4. The conductive nanoparticle formulation as claimed in claim 1 , wherein the reducing agent is selected from the group consisting of diethanolamine, triethanolamine, ethylene glycol, polyethylene glycol, ascorbic acid, sodium borohydride, sodium citrate, ascorbate and mixtures therefrom.

5. The conductive nanoparticle formulation as claimed in claim 1 , wherein the stabilizer is selected from the group consisting of polyvinyl pyrrolidone, polyvinylidene fluoride, polyvinyl alcohol, polyethylene glycol, citrate, gelatin, chitosan and mixtures therefrom.

6. The conductive nanoparticle formulation as claimed in claim 1 , wherein the primary encapsulating agent is polyacrylic acid.

7. The conductive nanoparticle formulation as claimed in claim 1 , wherein the secondary encapsulating agent is polyvinylpyrrolidone.

8. The conductive nanoparticle formulation as claimed in claim 1 , wherein the UV monomer resin is selected from the group consisting of polyethylene glycol) monoacrylate, polyethylene glycol) diacrylate, polyethylene glycol) triacrylate and mixtures therefrom.

9. The conductive nanoparticle formulation as claimed in claim 1 , wherein the solvent is selected from the group consisting of deionized water, ethanol, acetone, isopropyl, dioxane, ethylene glycol, ethylamine, water miscible solvent and mixtures therefrom.

10. An ink formulation for inkjet printing, wherein the ink formulation comprises the conductive nanoparticle formulation as claimed in claim 1 .

11 . A method of preparing conductive nanoparticle formulation, wherein the method comprises the steps of: i. adding primary encapsulating agent and secondary encapsulating agent into stabilizer while stirring to produce a copolymer at a temperature ranging between 25°C to 30°C for a duration ranging between 30 minutes to 1 hour; ii. adding silver precursor into reducing agent dropwise while stirring to produce a reduced silver colloidal solution at a temperature ranging between 25°C to 30°C until the colour of the reduced silver colloidal solution turn into light yellow; iii. adding the copolymer obtained from step (i) into the reduced silver colloidal solution obtained from step (ii) while stirring to produce a first mixture at a temperature ranging between 25°C to 30°C for a duration ranging between 8 hours to 10 hours; iv. adding UV monomer resin into the first mixture obtained from step (iii) while stirring to produce a second mixture at a temperature ranging between 25°C to 120°C for a duration ranging between 2 hours to 10 hours; v. stirring the second mixture obtained from step (iv) to produce homogenous second mixture at a temperature ranging between 25°C to 30°C for a duration ranging between 12 hours to 24 hours; vi. ultrasonicating the homogenous second mixture obtained from step (v) to produce a third mixture at temperature ranging between 50^sC to 70^sC for a duration ranging between 40 minutes to 60 minutes; vii. adding a solvent into the third mixture obtained from step (vi) in a ratio ranging between 1 :9 to 1 .8:8.2 while stirring to produce a fourth mixture at a temperature ranging between 25°C to 30°C for a duration ranging between 0.5 hours to 1 hour; viii. centrifuging the fourth mixture obtained from step (vii) at least once to obtain supernatant at a temperature ranging between 25°C to 30°C for a duration ranging between 10 minutes to 20 minutes; ix. adding a solvent into the supernatant obtained from step (viii) in a ratio ranging between 1 :9 to 3:7 while stirring to produce a fifth mixture at a temperature ranging between 25°C to 30°C for a duration ranging between 5 minutes to 30 minutes; and x. ultrasonicating the fifth mixture obtained from step (ix) to produce conductive nanoparticle formulation at a temperature ranging between 20^sC to 25^SC for a duration ranging between 30 minutes to 90 minutes.