Preparation method of polyurethane conductive ink based on ionic liquid modified graphene

Abstract

The invention provides a preparation method of polyurethane conductive ink based on ionic liquid modified graphene, and belongs to the technical field of conductive ink. Firstly, graphene oxide (GO) is subjected to non-covalent modification through ionic liquid, so that the dispersity and polyurethane affinity of the graphene oxide (GO) are improved; and then, uniformly mixing the modified graphene with a waterborne polyurethane emulsion by adopting an emulsion blending method to form the stable conductive ink. The ink has excellent conductivity, flexibility and adhesive force, and is suitable for flexible electronic devices, printed electronics, antistatic coatings and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive inks, and in particular to a preparation method of a polyurethane conductive ink based on ionic liquid-modified graphene. Background Art

[0002] Conductive ink is a functional ink containing conductive fillers, which is widely used in fields such as flexible electronics, printed electronics, electromagnetic shielding, antistatic coatings, and intelligent sensors. Traditional conductive inks mainly use materials such as silver nanoparticles, carbon nanotubes (CNTs), and graphene as conductive fillers. Among them, although silver-based conductive inks have excellent conductivity, they are expensive and vulnerable to oxidation, which limits their large-scale application. In contrast, carbon-based materials, such as graphene, have become one of the research hotspots of conductive inks in recent years due to their excellent conductivity, mechanical strength, chemical stability, and low cost.

[0003] However, the dispersion problem of graphene in the polymer matrix limits its application in conductive inks. Graphene has strong π-π interactions and hydrophobicity, and is prone to agglomeration in solution, resulting in a decrease in the conductivity of the ink and affecting the uniformity of film formation. To improve the dispersion of graphene in the aqueous polyurethane (WPU) matrix, chemical modification methods are usually adopted, including covalent bond modification (such as redox method, functional group grafting) and non-covalent bond modification (such as surfactant adsorption, polymer coating).

[0004] Among them, covalent bond modification (such as functionalizing graphene with carboxyl, hydroxyl, or epoxy groups) can enhance the compatibility between graphene and polymers, but usually destroys its sp² conjugated structure, thereby reducing its conductivity. Non-covalent modification (such as surfactant adsorption) has the problem of weak interfacial force, resulting in easy re-agglomeration of graphene in the matrix and affecting the conductive stability of the ink. Therefore, how to improve the dispersion and compatibility of graphene in aqueous polyurethane while maintaining its excellent conductive performance has become a key technical problem in this field. Summary of the Invention

[0005] Based on this background, the present invention proposes a preparation method of a polyurethane conductive ink based on ionic liquid-modified graphene. By using ionic liquid for non-covalent modification of graphene, its water solubility and dispersion stability in polyurethane emulsion are improved. Subsequently, a high-stability and high-conductivity conductive ink is prepared by emulsion blending method.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A preparation method of a polyurethane conductive ink based on ionic liquid-modified graphene, characterized in that it includes the following components (by mass parts): Graphene Oxide (GO): 0.5 - 3 parts; Ionic liquid: 0.5 - 5 parts; Deionized water: 50 - 150 parts; Waterborne polyurethane emulsion (WPU): 90 - 98 parts; Wetting agent: 0.2 - 1.5 parts; Leveling agent: 0.1 - 1 part; Defoaming agent: 0.1 - 1 part.

[0007] In the present invention, the sheet size of the graphene oxide (GO) is controlled within 200 nm - 5 μm, and the oxygen content is 25 - 40 wt%.

[0008] In the present invention, the ionic liquid is 1 - hydroxyethyl - 3 - methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl, and its preparation method includes the following steps: Add 200 - 300 parts of toluene into a three - necked flask equipped with a magnetic stirrer, a thermometer and a reflux condenser, start stirring, and add 21 - 42 parts of 1 - hydroxyethyl - 3 - methylimidazolium tetrafluoroborate; add 0.2 - 0.5 part of organotin, and stir evenly; add 5 - 10 parts of 3 - thiophene isocyanate and 0.2 - 2 parts of 2 - (4 - biphenyl) ethyl isocyanate into a constant - pressure dropping funnel, and slowly drop them into the three - necked flask, with the dropping time being 1 - 2 hours; after the dropping is completed, raise the temperature of the reaction system to 80 - 90 °C, and carry out reflux reaction for 3 - 6 hours. After drying, 1 - hydroxyethyl - 3 - methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl is obtained.

[0009] In the present invention, the organotin is selected from at least one of dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctanoate, and dibutyltin dilaurate ester.

[0010] In the present invention, the wetting agent is selected from BYK - 333 or FC - 4430 or a combination thereof.

[0011] In the present invention, the leveling agent is selected from TEGO - 270 or BYK - 310 or a combination thereof.

[0012] In the present invention, the defoaming agent is selected from TEGO - 825 or BYK - 012 or a combination thereof.

[0013] In the present invention, the preparation method of the ink: (1) Pretreatment and modification of GO: Modify GO with the ionic liquid prepared by this method (IL - GO) for standby; (2) Mix the WPU emulsion: Take 90 - 98 parts of WPU emulsion and stir for 30 minutes at room temperature of 25 °C; (3) Add modified GO: Under stirring, slowly add 0.5 - 3 parts of IL-GO suspension, and keep stirring at 500 - 1000 rpm for 1 - 3 hours; (4) Add additives: Add wetting agent, leveling agent, and defoaming agent in sequence, and continue stirring for 30 - 60 minutes to ensure uniform mixing; (5) Grinding: Use a three-roll mill or ball mill to grind at 1000 - 3000 rpm for 2 - 4 times to ensure uniform dispersion of GO and prevent agglomeration; (6) Filtration: Filter with a 200 - 400 mesh filter cloth to remove large particles and obtain a uniform and stable conductive ink.

[0014] In the present invention, the method for modifying GO with ionic liquid includes the following steps: (1) Ultrasonic dispersion of GO: Add 0.5 - 3 parts of GO into 50 - 150 parts of deionized water, and ultrasonically treat at 25 - 50 °C for 30 - 90 minutes to obtain a uniform suspension; (2) Add ionic liquid for reaction: Slowly drop 0.5 - 5 parts of ionic liquid into the above-mentioned GO suspension, stir magnetically for 1 - 3 hours, and the reaction temperature is 30 - 60 °C to ensure that the ionic liquid is uniformly adsorbed on the surface of GO; (3) Ultrasonic stabilization: Perform ultrasonic treatment on the reaction product at 40 kHz for 30 - 60 minutes to further improve the dispersibility of GO.

[0015] Reaction principle The hydroxyl group (-OH) in 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate reacts with the isocyanate group (-NCO) in 3-thiophene isocyanate and 2-(4-biphenyl)ethyl isocyanate to form a urethane bond (-NHCOO-), and organotin acts as a catalyst to accelerate the reaction, and toluene acts as a solvent to provide a reaction environment.

[0016] Beneficial effects The 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl prepared in the present invention has good conductivity and dispersibility. The π-electron cloud of thiophene and the large π-bond of graphene have π-π interaction, which promotes charge transfer and reduces resistance. The conjugated system participates in forming a conductive channel and increases the electron migration force. The large conjugate and rigid structure of biphenyl combine with graphene through π-π stacking to form a stable conductive network, expand the electron delocalization and improve the mobility, making the charge conduction smoother.

[0017] Improvement of dispersibility Thiophene and biphenyl increase the steric hindrance and polarity of the ionic liquid molecules, making it better adsorbed on the surface of graphene to form a coating layer, preventing the aggregation of graphene sheets; the good solubility of the ionic liquid helps the uniform dispersion of graphene in the ink solvent, ensuring the stability and consistency of the ink.

[0018] Enhancement of Stability Thiophene and biphenyl endow the ionic liquid with chemical stability, resisting external factors such as oxidation and hydrolysis, and protecting graphene; the ionic liquid interacts with graphene to form a stable complex, making the conductive ink stable in storage and use and extending its service life. Specific Embodiments

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without any creative work shall fall within the protection scope of the present invention.

[0020] Example 1 Steps for Preparing Ink: (1) Pretreatment and modification of GO (IL-GO): Take 1.5 g of graphene oxide (GO) with a sheet size controlled at 3 μm and an oxygen content of 30 wt%, add it to 100 g of deionized water, and ultrasonicate for 60 minutes at 40 °C to obtain a uniform suspension.

[0021] Slowly drop 0.5 g of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl into the GO suspension, stir magnetically for 2 hours, and the reaction temperature is 45 °C. Ultrasonically treat the reaction product at 40 kHz for 45 minutes to obtain IL-GO for standby.

[0022] Preparation method of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl: Add 250 g of toluene to a three-necked flask equipped with a magnetic stirrer, a thermometer, and a reflux condenser, and start the stirring device. Subsequently, add 30 g of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate and 0.3 g of dibutyltin dilaurate to ensure uniform mixing of the mixture. Then, slowly drop 7 g of 3-thiophene isocyanate and 1 g of 2-(4-biphenyl)ethyl isocyanate into the three-necked flask through a constant-pressure dropping funnel, and the dropping process lasts for 1.5 hours. After the dropping is completed, raise the temperature of the reaction system to 85 °C and reflux and react at this temperature for 4 hours. Finally, dry the reaction product to obtain 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl.

[0023] (2) Mix the WPU emulsion: Take 95 g of waterborne polyurethane emulsion (WPU) and stir for 30 minutes at room temperature of 25 °C.

[0024] (3) Add the modified GO: Under stirring, slowly add 1.5 g of IL-GO suspension and keep stirring at 800 rpm for 2 hours.

[0025] (4) Adding additives and subsequent treatment: Add 0.8 g of wetting agent BYK-333, 0.5 g of leveling agent TEGO-270, and 0.5 g of defoaming agent TEGO-825 in sequence, and continue stirring for 45 minutes.

[0026] Use a three-roll mill to grind 3 times at 2000 rpm.

[0027] Filter with a 300-mesh filter cloth to obtain a uniform and stable conductive ink.

[0028] Example 2 Steps for preparing the ink: (1) Pretreatment of modified GO (IL-GO): Take 0.5 g of graphene oxide (GO) with a sheet size of 200 nm and an oxygen content of 25 wt%, add it to 50 g of deionized water, and ultrasonicate for 30 minutes at 25 °C.

[0029] Use the prepared ionic liquid, slowly add 2 g dropwise to the GO suspension, stir magnetically for 1 hour, and the reaction temperature is 30 °C. Ultrasonicate for 30 minutes to obtain IL-GO.

[0030] Preparation method of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl: In a three-necked flask equipped with a magnetic stirrer, temperature monitor, and reflux condenser, first add 200 g of toluene and start stirring. Then, add 21 g of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate and add 0.2 g of dibutyltin diacetate to ensure uniform mixing. Through a constant-pressure dropping funnel, slowly add 5 g of 3-thiophene isocyanate and 0.2 g of 2-(4-biphenyl)ethyl isocyanate to the three-necked flask, and control the dropping time within 1 hour. After the dropping is completed, raise the temperature to 80 °C and reflux for 3 hours. Finally, perform drying treatment to obtain the target ionic liquid.

[0031] (2) Mixing WPU emulsion: Take 90 g of WPU emulsion and stir for 30 minutes.

[0032] (3) Adding modified GO: Add 0.5 g of IL-GO suspension and keep stirring at 500 rpm for 1 hour.

[0033] (4) Adding additives and subsequent treatment: Add 0.2 g of FC-4430 as a wetting agent, 0.1 g of BYK-310 as a leveling agent, and 0.1 g of BYK-012 as a defoaming agent, and stir for 30 minutes.

[0034] Use a ball mill to grind twice at 1000 rpm.

[0035] Filter with a 200-mesh filter cloth to obtain the ink.

[0036] Example 3 Steps for preparing the ink: (1) Pretreat and modify GO (IL-GO): Take 3 g of GO with a sheet size controlled at 5 μm and an oxygen content of 40 wt%, add it to 150 g of deionized water, and ultrasonicate for 90 minutes at 50 °C.

[0037] Use the prepared ionic liquid, slowly drop 3.5 g into the GO suspension, stir magnetically for 3 hours at a reaction temperature of 60 °C, and ultrasonicate for 60 minutes.

[0038] Preparation method of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl: Take 300 g of toluene and place it in a three-necked flask equipped with a magnetic stirrer, a thermometer, and a reflux condenser, and start stirring. Then, add 42 g of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate and mix in 0.5 g of dibutyltin dilaurate to ensure uniform stirring of the mixture. Next, use a constant-pressure dropping funnel to slowly drop 10 g of 3-thiophene isocyanate and 2 g of 2-(4-biphenyl)ethyl isocyanate into the three-necked flask, and the dropping process takes 2 hours. After the dropping is complete, heat the reaction system to 90 °C and maintain this temperature for reflux reaction for 6 hours. Finally, dry the reaction product to obtain the ionic liquid containing specific functional groups.

[0039] (2) Mix the WPU emulsion: Take 98 g of the WPU emulsion and stir for 30 minutes.

[0040] (3) Add the modified GO: Add 3 g of the IL-GO suspension and stir at 1000 rpm for 3 hours.

[0041] (4) Add additives and subsequent treatment: Add 1.5 g of a mixture of BYK-333 and FC-4430 wetting agents, 1 g of a mixture of TEGO-270 and BYK-310 leveling agents, and 1 g of a mixture of TEGO-825 and BYK-012 defoaming agents, and stir for 60 minutes.

[0042] Use a three-roll mill to grind 4 times at 3000 rpm.

[0043] Filter with a 400-mesh filter cloth.

[0044] Example 4 Steps for preparing the ink: (1) Pretreatment and modification of GO (IL-GO): Take 2 g of GO with a sheet size controlled at 1 μm and an oxygen content of 35 wt%, add it to 100 g of deionized water, and ultrasonicate for 45 minutes at 40 °C.

[0045] Using the prepared ionic liquid, slowly add 5 g to the GO suspension, stir magnetically for 2 hours at a reaction temperature of 50 °C, and ultrasonicate for 45 minutes.

[0046] Preparation method of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl: Add 275 g of toluene to a three-necked flask equipped with magnetic stirring, temperature monitoring, and reflux condensation equipment, and then start stirring. Next, add 35 g of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate and 0.4 g of dibutyltin dilaurate to ensure the mixture is homogeneous. Through a constant-pressure dropping funnel, slowly add 8 g of 3-thiophene isocyanate and 1.5 g of 2-(4-biphenyl)ethyl isocyanate to the three-necked flask over a period of about 1.5 hours. After the addition is complete, raise the temperature to 88 °C and reflux for 5 hours at this temperature. Finally, dry the reaction product to obtain the desired ionic liquid.

[0047] (2) Mixing WPU emulsion: Take 92 g of WPU emulsion and stir for 30 minutes.

[0048] (3) Adding modified GO: Add 2 g of IL-GO suspension and stir at 700 rpm for 2 hours.

[0049] (4) Adding additives and subsequent treatment: Add 1 g of BYK-333 as a wetting agent, 0.8 g of TEGO-270 as a leveling agent, and 0.8 g of TEGO-825 as an antifoaming agent, and stir for 45 minutes.

[0050] Use a ball mill to grind 3 times at 2000 rpm.

[0051] Filter through a 300-mesh filter cloth to obtain the ink.

[0052] Comparative Example 1 The difference from Example 1 is that 3-thiophene isocyanate is not added during the preparation of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl.

[0053] Comparative Example 2 The difference from Example 1 is that 2-(4-biphenyl)ethyl isocyanate is not added during the preparation of 1-hydroxyethyl-3-methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl.

[0054] Test method (1) Conductivity test (four-probe method) Test standard: The four-probe method (ASTM D 4496-13) is adopted, and a digital four-probe resistance tester (Keithley 2400) is used to measure the surface conductivity (S / m) of the thin film.

[0055] Test conditions: The ink is evenly coated on a PET substrate (thickness 10 μm), and after drying, the surface resistance is tested and the conductivity is calculated.

[0056] (2) Storage stability test (accelerated aging experiment) Test standard: The accelerated aging test is carried out in accordance with ISO 4623-2 to investigate the stability of the ink after being in a high-temperature and high-humidity environment (50°C, 85% RH, 30 days) and long-term storage (6 months, 25°C).

[0057] Test conditions: Observe whether the ink shows delamination, sedimentation, and viscosity changes, and measure the change rate of conductivity before and after storage (Δσ / σ0).

[0058] (3) Flexibility durability test (180° bending durability) Test standard: In accordance with the IEC 62047-3 standard, the PET flexible circuit board with a conductive ink coating is subjected to a 180° bending test to monitor the resistance change.

[0059] Test conditions: 1,000 bending cycles (bending radius R = 2 mm), and measure the resistance change before and after bending (ΔR / R0).

[0060] Table 1 Test results: Conductivity (S / m) <![CDATA[Change in conductivity after 6 months of storage (Δσ / σ0)]]> <![CDATA[Resistance change (ΔR / R0) after 1000 times of bending]]> Example 1 1.95× 10³ 3.1% 1.7% Example 2 2.03× 10³ 2.9% 1.5% Example 3 2.12× 10³ 2.8% 1.4% Example 4 2.17× 10³ 2.6% 1.2% Comparative Example 1 1.90× 10³ 3.5% 2.3% Comparative Example 2 1.92× 10³ 3.4% 2.1% The ionic liquid-modified graphene conductive ink of the present invention is significantly superior to the unmodified GO ink in terms of conductivity, flexibility, and storage stability, meeting the application requirements of high-performance flexible electronics and printed electronics.

[0061] The above is only the preferred specific implementation manner of the present invention, and the protection scope of the present invention is not limited thereto. Any simple changes or equivalent replacements of the technical solutions that can be obviously obtained by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope of the present invention.

Claims

1. A preparation method of a polyurethane conductive ink based on ionic liquid modified graphene, characterized in that, Comprising the following components (by mass parts): Graphene oxide (GO): 0.5 - 3 parts; Ionic liquid: 0.5 - 5 parts; Deionized water: 50 - 150 parts; Waterborne polyurethane emulsion (WPU): 90 - 98 parts; Wetting agent: 0.2 - 1.5 parts; Leveling agent: 0.1 - 1 part; Defoaming agent: 0.1 - 1 part; The ionic liquid is 1 - hydroxyethyl - 3 - methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl, and is prepared by reacting 1 - hydroxyethyl - 3 - methylimidazolium tetrafluoroborate, 3 - thiophene isocyanate, and 2-(4 - biphenyl)ethyl isocyanate.

2. The preparation method of a polyurethane conductive ink based on ionic liquid modified graphene according to claim 1, characterized in that: The sheet size of the graphene oxide (GO) is controlled within 200 nm - 5 μm, and the oxygen content is 25 - 40 wt%.

3. The preparation method of a polyurethane conductive ink based on ionic liquid modified graphene according to claim 1, characterized in that: The ionic liquid is 1 - hydroxyethyl - 3 - methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl, and its preparation method includes the following steps: Add 200 - 300 parts of toluene into a three - necked flask equipped with a magnetic stirrer, a thermometer, and a reflux condenser. Start stirring and add 21 - 42 parts of 1 - hydroxyethyl - 3 - methylimidazolium tetrafluoroborate; add 0.2 - 0.5 part of organotin and stir evenly; add 5 - 10 parts of 3 - thiophene isocyanate and 0.2 - 2 parts of 2-(4 - biphenyl)ethyl isocyanate into a constant - pressure dropping funnel, and slowly drop them into the three - necked flask. The dropping time is 1 - 2 hours; after the dropping is completed, raise the temperature of the reaction system to 80 - 90 °C and reflux for 3 - 6 hours. After drying, obtain 1 - hydroxyethyl - 3 - methylimidazolium tetrafluoroborate ionic liquid containing thiophene and biphenyl.

4. The preparation method of a polyurethane conductive ink based on ionic liquid modified graphene according to claim 3, characterized in that: The organotin is selected from at least one of dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctanoate, and dibutyltin dilaurate.

5. The preparation method of a polyurethane conductive ink based on ionic liquid modified graphene according to claim 1, characterized in that: The wetting agent is selected from BYK - 333 or FC - 4430 or a combination thereof.

6. The preparation method of a polyurethane conductive ink based on ionic liquid modified graphene according to claim 1, characterized in that: The leveling agent is selected from TEGO - 270 or BYK - 310 or a combination thereof.

7. The preparation method of a polyurethane conductive ink based on ionic liquid modified graphene according to claim 1, characterized in that: The defoaming agent is selected from TEGO - 825 or BYK - 012 or a combination thereof.

8. The preparation method of a polyurethane conductive ink based on ionic liquid modified graphene according to claim 1, characterized in that: The preparation method of the ink: (1) Pretreatment and modification of GO: Modify GO with the ionic liquid prepared by this method (IL - GO) and set aside; (2) Mix WPU emulsion: Take 90 - 98 parts of WPU emulsion and stir at room temperature of 25 °C for 30 minutes; (3) Add modified GO: Under stirring, slowly add 0.5 - 3 parts of IL - GO suspension and keep stirring at 500 - 1000 rpm for 1 - 3 hours; (4) Add additives: Add the wetting agent, leveling agent, and defoaming agent in sequence, and continue stirring for 30 - 60 minutes to ensure uniform mixing; (5) Grinding: Use a three - roll mill or a ball mill to grind at 1000 - 3000 rpm for 2 - 4 times to ensure uniform dispersion of GO and prevent agglomeration; (6) Filtration: Filter with a 200 - 400 - mesh filter cloth to remove large particles and obtain a uniform and stable conductive ink.

9. The preparation method of a polyurethane conductive ink based on ionic liquid modified graphene according to claim 8, characterized in that: The method for modifying GO with the ionic liquid includes the following steps: (1) Ultrasonic dispersion of GO: Add 0.5 - 3 parts of GO into 50 - 150 parts of deionized water and ultrasonicate at 25 - 50 °C for 30 - 90 minutes to obtain a uniform suspension; (2)Ionic liquid addition reaction: Slowly add 0.5 - 5 parts of ionic liquid to the above-mentioned GO suspension, stir magnetically for 1 - 3 hours, and the reaction temperature is 30 - 60 °C to ensure that the ionic liquid is evenly adsorbed on the surface of GO; (3)Ultrasonic stabilization: Ultrasonically treat the reaction product at 40 kHz for 30 - 60 minutes to further improve the dispersibility of GO.