Printable electrode paste for flexible electronic device and preparation method of printable electrode paste

Abstract

The invention discloses printable electrode slurry for a flexible electronic device and a preparation method of the printable electrode slurry, and belongs to the technical field of electrode slurry, and the printable electrode slurry comprises flaky tungsten powder, mesoporous silica, fibrous magnesium oxide powder, a defoaming agent, a leveling agent and the balance of a waterborne polyurethane binder. According to the flaky tungsten powder, a continuous conductive network is formed through surface contact, and the seepage threshold value is reduced; the mesoporous silica is used as a flexible buffer phase and can absorb more than 90% of bending stress; the silicon dioxide-magnesium oxide composite ceramic phase is cured at 180 DEG C to form a compact framework, so that the resistance fluctuation of the slurry under the thermal cycle of-40 DEG C to 150 DEG C is less than 3%, and the resistance increase is less than 8% after the slurry is aged for 500 hours at the humidity of 85 DEG C / 85%.

Description

Technical Field

[0001] This invention relates to the field of electrode paste technology, and in particular to a printable electrode paste for flexible electronic devices and its preparation method. Background Technology

[0002] In the prior art, printable electrode pastes suitable for flexible substrates (such as polyethylene terephthalate (PET) and polyimide (PI)) are widely used in flexible displays, wearable sensors, and electronic skin.

[0003] In existing printed electrode pastes, such as silver paste with a silver content of 85%, the sheet resistance can be as low as 0.2Ω, but the cost is high and the bending performance is poor, with the resistance increasing by more than 30% after 500 bends. Using carbon nanotube composite paste can reduce the cost by 50% compared to silver paste, but the conductivity is insufficient (sheet resistance greater than 2Ω / □) and the adhesion to flexible substrates is poor (3B grade). As for copper powder paste, copper is easily oxidized, and the sheet resistance increases by 50% in 7 days under 60% humidity, requiring the addition of antioxidants, which complicates the process. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a printable electrode paste for flexible electronic devices and a method for preparing the same, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] This invention discloses a printable electrode paste for flexible electronic devices, wherein the printable electrode paste comprises, by weight percentage:

[0007] The composition consists of 30%–40% flake tungsten powder, 20%–30% mesoporous silica, 5%–10% fibrous magnesium oxide powder, 0.5%–1% defoamer, 0.2%–0.5% leveling agent, and the remainder is water-based polyurethane binder. The aspect ratio of the flake tungsten powder is 8:1–12:1, and the pore size of the mesoporous silica is 5–10 nm.

[0008] Preferably, the aspect ratio of the fibrous magnesium oxide powder is greater than 20, which is used to improve the flexural fatigue resistance of the slurry.

[0009] Another aspect of the present invention discloses a method for preparing the above-mentioned printable electrode paste for flexible electronic devices, the method comprising the following steps:

[0010] S1: Add flaky tungsten powder and fibrous magnesium oxide powder to a planetary ball mill for premixing to improve dispersion uniformity. The ball-to-material ratio of the planetary ball mill is 3:1, the rotation speed is 200 rpm, and the premixing time is 1 to 1.5 hours.

[0011] S2: Dry the mesoporous silica at 120°C for 2-2.5 hours to remove adsorbed moisture;

[0012] S3: The dried mesoporous silica, premixed flake tungsten powder, and fibrous magnesium oxide powder are added to the water-based polyurethane binder and ground three times with a three-roll mill to form a uniform slurry. The roller spacing of the three-roll mill is 10μm and the rotation speed is 50rpm.

[0013] S4: Add defoamer and leveling agent, then stir for 30-40 minutes to form a printable electrode paste;

[0014] S5: The printable electrode paste is screen-printed onto a PET or PI substrate with a thickness of 15-20 μm and a mesh count of 250-300.

[0015] S6: Perform step curing in a hot air circulating oven. First, pre-bake at 80-100℃ for 10 minutes, and then perform main curing at 150-180℃ for 20 minutes to avoid deformation of the PET or PI substrate.

[0016] Preferably, the defoamer is a polyether-modified siloxane, and the leveling agent is an acrylate.

[0017] Preferably, the printable electrode paste is suitable for screen printing or inkjet printing.

[0018] Preferably, the sheet resistance of the printed electrode paste after curing is less than or equal to 0.6Ω / □, and the resistance change after 1000 bends is less than 5%.

[0019] The above technical solution has the following beneficial effects:

[0020] High conductivity and low percolation threshold:

[0021] The sheet tungsten powder of this application forms a continuous conductive network through surface contact, reducing the percolation threshold to 25% and achieving a sheet resistance of 0.5Ω with 35% tungsten content, which is close to the performance of silver paste (0.2Ω), but the cost is only 1 / 7 of that of silver paste.

[0022] Superior flexibility and bending resistance:

[0023] In this application, mesoporous silica is used as a flexible buffer phase, which can absorb more than 90% of bending stress; magnesium oxide fiber enhances fracture resistance through bridging, and its resistance only increases by 4% after 1000 bends, which is better than silver paste and carbon paste.

[0024] High temperature resistance and weather resistance:

[0025] The silica-magnesium oxide composite ceramic phase of this application forms a dense skeleton after curing at 180℃, which makes the resistance fluctuation of the slurry less than 3% under thermal cycling from -40℃ to 150℃, and the resistance increase is less than 8% after aging at 85℃ / 85% humidity for 500h, which is superior to copper-based slurry.

[0026] Environmental friendliness and process compatibility:

[0027] This application presents a waterborne polyurethane adhesive that enables solvent-free printing, has a curing temperature of less than or equal to 180°C, is suitable for heat-sensitive substrates such as PET / PI, and does not require inert atmosphere protection, making it suitable for roll-to-roll mass production. Detailed Implementation

[0028] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] The main purpose of this application is to: replace precious metals (such as silver) in the prior art with flake tungsten powder, form a conductive network through a high aspect ratio structure, and reduce the percolation threshold; use mesoporous silica as a flexible buffer phase to absorb bending stress, and use magnesium oxide fibers to enhance mechanical strength; and use water-based polyurethane adhesive to achieve environmentally friendly printing with a low curing temperature (≤180℃), which is suitable for heat-sensitive substrates.

[0030] Example 1

[0031] A printable electrode paste for flexible electronic devices, comprising, by weight percentage:

[0032] The composition consists of 30%–40% flake tungsten powder, 20%–30% mesoporous silica, 5%–10% fibrous magnesium oxide powder, 0.5%–1% defoamer, 0.2%–0.5% leveling agent, and the remainder is water-based polyurethane binder. The aspect ratio of the flake tungsten powder is 8:1–12:1, and the pore size of the mesoporous silica is 5–10 nm.

[0033] Specifically, the printable electrode paste, by weight percentage, comprises: 30%–40% flake tungsten powder, 20%–30% mesoporous silica, 5%–10% fibrous magnesium oxide powder, 0.5%–1% defoamer, 0.2%–0.5% leveling agent, and the remainder being water-based polyurethane binder. The total weight percentage of flake tungsten powder, mesoporous silica, fibrous magnesium oxide powder, defoamer, leveling agent, and water-based polyurethane binder is 100%. Specifically, by weight percentage, the printable electrode paste comprises: 35% flake tungsten powder, 25% mesoporous silica, 8% fibrous magnesium oxide powder, 0.8% defoamer, 0.3% leveling agent, and 30.9% water-based polyurethane binder. The aspect ratio of the flake tungsten powder is 8:1 or 12:1, and can also be 10:1. The pore size of the mesoporous silica is 5 mm. nm or 10 nm, and the aperture can also be 7 nm;

[0034] In other embodiments of this example, the printable electrode paste comprises, by weight percentage: 30% flake tungsten powder, 20% mesoporous silica, 5% fibrous magnesium oxide powder, 0.5% defoamer, 0.2% leveling agent, and 44.3% waterborne polyurethane binder.

[0035] In other embodiments of this example, the printable electrode paste may further include, by weight percentage: 40% flake tungsten powder, 30% mesoporous silica, 10% fibrous magnesium oxide powder, 1% defoamer, 0.5% leveling agent, and 18.5% waterborne polyurethane binder.

[0036] In some embodiments, the aspect ratio of fibrous magnesium oxide powder is greater than 20, which is used to improve the bending fatigue resistance of the paste. The magnesium oxide fibers enhance the fracture resistance through bridging. After 1000 bends, the resistance only increases by 4%, which is better than silver paste and carbon paste.

[0037] Waterborne polyurethane adhesives enable solvent-free printing, have a curing temperature of 180°C or less, are suitable for heat-sensitive substrates such as PET / PI, and do not require inert atmosphere protection, making them suitable for roll-to-roll mass production.

[0038] Example 2

[0039] A method for preparing a printable electrode paste for flexible electronic devices includes the following steps:

[0040] S1: Add flaky tungsten powder and fibrous magnesium oxide powder to a planetary ball mill for premixing to improve dispersion uniformity. The ball-to-material ratio of the planetary ball mill is 3:1, the rotation speed is 200 rpm, and the premixing time is 1 to 1.5 hours.

[0041] Specifically, the amounts of flaky tungsten powder and fibrous magnesium oxide powder in the printable electrode paste are weighed out and then added to a planetary ball mill for premixing. The ball-to-material ratio of the planetary ball mill is set to 3:1, the rotation speed is set to 200 rpm, and the premixing time is 1 hour or 1.5 hours to complete the premixing.

[0042] Flake tungsten powder forms a continuous conductive network through surface contact, reducing the percolation threshold to 25% and achieving a sheet resistance of 0.5Ω with 35% W content, which is close to the performance of silver paste (0.2Ω), but the cost is only 1 / 7 of that of silver paste. It has high conductivity and low percolation threshold.

[0043] S2: Dry the mesoporous silica at 120°C for 2-2.5 hours to remove adsorbed moisture;

[0044] Specifically, mesoporous silica is dried at 120°C for 2 hours or 2.5 hours using a dryer at 120°C to remove adsorbed moisture from the mesoporous silica.

[0045] Mesoporous silica, as a flexible buffer phase, can absorb more than 90% of bending stress; magnesium oxide fiber enhances fracture resistance through bridging, and its resistance only increases by 4% after 1000 bends, which is better than silver paste and carbon nanotube (CNT) composite paste, and has super flexibility and bending resistance.

[0046] S3: The dried mesoporous silica, premixed flake tungsten powder, and fibrous magnesium oxide powder are added to the water-based polyurethane binder and ground three times with a three-roll mill to form a uniform slurry. The roller spacing of the three-roll mill is 10μm and the rotation speed is 50rpm.

[0047] Specifically, the dried mesoporous silica, along with the premixed flake tungsten powder and fibrous magnesium oxide powder, is added to the water-based polyurethane binder and then ground three times using a three-roll mill to form a uniform slurry.

[0048] After curing at 180℃, the silica-magnesium oxide composite ceramic phase forms a dense skeleton, which makes the resistance fluctuation of the slurry less than 3% under thermal cycling from -40℃ to 150℃, and the resistance increase is less than 8% after aging at 85℃ / 85% humidity for 500h, which is superior to copper-based slurries and has high temperature resistance and weather resistance.

[0049] S4: Add defoamer and leveling agent, then stir for 30-40 minutes to form a printable electrode paste;

[0050] Specifically, add 0.5% to 1% of defoamer and 0.2% to 0.5% of leveling agent to the above uniform slurry. The defoamer is polyether-modified siloxane and the leveling agent is acrylate. The specific amount added is determined according to the above slurry ratio. Then stir for 30 minutes or 40 minutes to form a printable electrode slurry.

[0051] S5: The printable electrode paste is screen-printed onto a PET or PI substrate to a thickness of 15–20 μm, with a screen mesh count of 250–300 mesh. Specifically, the printable electrode paste is screen-printed onto a PET or PI substrate, wherein the PET substrate is made of polyethylene terephthalate (PET) material and the PI substrate is made of polyimide (PI) material, with a coating thickness of 15 μm or 20 μm and a screen mesh count of 250 or 300 mesh.

[0052] S6: Perform step curing in a hot air circulating oven. First, pre-bake at 80-100℃ for 10 minutes, and then perform main curing at 150-180℃ for 20 minutes to avoid deformation of the PET substrate or PI substrate.

[0053] Specifically, after the printable electrode paste is coated, it is dried in a hot air circulating oven. The PET substrate or PI substrate is placed in the hot air circulating oven and heated. When the temperature reaches 80°C or 100°C, it is pre-dried for 10 minutes. The temperature is then increased to 150°C or 180°C and dried and cured for 20 minutes. Finally, the temperature is reduced to room temperature to complete the drying process.

[0054] In some embodiments, the printable electrode paste prepared by the above method is suitable for screen printing or inkjet printing, and the paste can be printed on the substrate by screen printing or inkjet printing.

[0055] In some embodiments, the sheet resistance of the printable electrode paste prepared by the above method after curing is less than or equal to 0.6 Ω / □, and the resistance change after 1000 bends is less than 5%, which is superior to the prior art.

[0056] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A printable electrode paste for flexible electronic devices, characterized in that, The printable electrode paste comprises, by weight percentage: The composition consists of 30%–40% flake tungsten powder, 20%–30% mesoporous silica, 5%–10% fibrous magnesium oxide powder, 0.5%–1% defoamer, 0.2%–0.5% leveling agent, and the remainder is water-based polyurethane binder. The aspect ratio of the flake tungsten powder is 8:1–12:1, and the pore size of the mesoporous silica is 5–10 nm.

2. The printable electrode paste for flexible electronic devices according to claim 1, characterized in that, The fibrous magnesium oxide powder has an aspect ratio greater than 20, which is used to improve the flexural fatigue resistance of the slurry.

3. A method for preparing a printable electrode paste for flexible electronic devices as described in any one of claims 1-2, characterized in that, The preparation method includes the following steps: S1: Add flaky tungsten powder and fibrous magnesium oxide powder to a planetary ball mill for premixing to improve dispersion uniformity. The ball-to-material ratio of the planetary ball mill is 3:1, the rotation speed is 200 rpm, and the premixing time is 1 to 1.5 hours. S2: Dry the mesoporous silica at 120°C for 2-2.5 hours to remove adsorbed moisture; S3: The dried mesoporous silica, premixed flake tungsten powder, and fibrous magnesium oxide powder are added to the water-based polyurethane binder and ground three times with a three-roll mill to form a uniform slurry. The roller spacing of the three-roll mill is 10μm and the rotation speed is 50rpm. S4: Add defoamer and leveling agent, then stir for 30-40 minutes to form a printable electrode paste; S5: The printable electrode paste is screen-printed onto a PET or PI substrate with a thickness of 15-20 μm and a mesh count of 250-300. S6: Perform step curing in a hot air circulating oven. First, pre-bake at 80-100℃ for 10 minutes, and then perform main curing at 150-180℃ for 20 minutes to avoid deformation of the PET or PI substrate.

4. The method for preparing printable electrode paste for flexible electronic devices according to claim 3, characterized in that, The defoamer is a polyether-modified siloxane, and the leveling agent is an acrylate.

5. The method for preparing printable electrode paste for flexible electronic devices according to claim 3, characterized in that, The printable electrode paste is suitable for screen printing or inkjet printing.

6. The method for preparing printable electrode paste for flexible electronic devices according to claim 3, characterized in that, The sheet resistance of the printed electrode paste after curing is less than or equal to 0.6Ω / □, and the resistance change is less than 5% after 1000 bends.