Revolutionizing Inkjet Printing: How Bead Mills Transform Graphene into High-Conductivity Inks

The current application of graphene in inkjet printing is the printing of conductive ink. The most popular application is graphene ink that can be used to print flexible circuit boards. Some companies are already selling this product.

Conductive ink was originally used for anti-static and electromagnetic shielding materials. Later, it was used to print circuits, batteries, capacitors, etc. Even future smart wearables may be directly printed.

Graphene ink prints out radio frequency antennas

Science and Technology Daily, Beijing, May 20 (Reporter Fang Linlin) Scientists have taken the application of graphene materials a big step forward. Researchers from the University of Manchester in the UK have collaborated with graphene manufacturer BGT Materials Co., Ltd. to print radio frequency antennas using compressed graphene ink. This antenna is flexible, environmentally friendly, and can be mass-produced cheaply. It can be used in wireless radio frequency identification (RFID) tags and wireless sensors. The results were published in the latest issue of Applied Physics Letters.

Since graphene was first isolated in 2004, its amazing properties have been extensively studied. The first commercial graphene product was conductive ink, which can be used to print circuits and other electronic components. Graphene ink is low-cost and very flexible, and has much stronger performance than other conductive inks such as nano-metal particles.

In order to make the graphene sheets dissolve better in the ink, a binder is sometimes added to help the ink solidify. This graphene ink must be annealed at high temperature before it can be used, but the annealing process will damage the material on which the graphene is printed - the paper or plastic surface.

Researchers have found a way to make graphene ink more conductive without the need for a binder. They first print it, then dry the ink, and then press it with a roller, much like a road roller repeatedly rolls over newly paved road surfaces.

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The results showed that the conductivity of the compressed ink increased by 50 times, and the graphene laminate was twice as fast as the previous graphene ink mixed with adhesive. "High conductivity makes wireless radio frequency radiation more efficient, which is the most exciting aspect of the experiment," said the researchers. Printing electronics on cheap and flexible materials such as paper and plastic means that wireless technologies such as RFID tags will become more ubiquitous, from a cow to a car part.

Currently, most commercial RFID tags are made of metal aluminum and copper, which are expensive and complex to make, while graphene-based RFID tags can significantly reduce material costs. The research team has already begun planning to develop graphene RFID tags, as well as sensors and wearable electronics.

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1. Preparation of Raw Materials

Graphite Source: Obtain high-quality graphite flakes as the starting material.

Solvent Selection: Choose a suitable solvent or dispersant. Common options include water, ethanol, or N-methyl-2-pyrrolidone (NMP), which helps suspend and stabilize graphene flakes.

Surfactants or Stabilizers: Additives like sodium dodecyl sulfate (SDS) or polyethylene glycol (PEG) can prevent reaggregation of graphene layers during processing.

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2. Setting Up the Bead Mill

Bead Selection: Use small, high-density beads (e.g., zirconia or silica) to achieve effective exfoliation. The bead size is typically between 0.1–0.5 mm.

Mill Type: Select a horizontal or vertical bead mill designed for high-shear grinding. Horizontal bead mills are often preferred for their consistency and ability to maintain stable processing conditions.

Operating Parameters:

Rotor Speed: High-speed rotation (e.g., 3000–8000 rpm) generates the necessary shear forces.

Flow Rate: Adjust the flow of the suspension to maintain a balance between processing time and heat dissipation.

Temperature Control: Incorporate a cooling system to prevent overheating, which could degrade the graphene quality.

3. Milling Process

Dispersion: Mix graphite, solvent, and stabilizers into the mill chamber.

Exfoliation: The high-energy collision of beads with graphite flakes exfoliates them into thin graphene layers.

Time Management: Typically, the process takes several hours to ensure uniform dispersion and minimal particle size.

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4. Filtration and Post-Treatment

Particle Size Control: Use filtration or centrifugation to remove oversized graphite particles or bead fragments.

Concentration Adjustment: If needed, concentrate the graphene ink by removing excess solvent or diluting it for specific viscosity suitable for inkjet printing.

Surface Modification: Add binders or surfactants to improve adhesion and conductivity for the final ink.

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5. Testing and Quality Assurance

Conductivity Measurement: Verify the electrical conductivity of the graphene ink to ensure it meets application requirements.

Viscosity Testing: Ensure the ink's viscosity is suitable for inkjet printer nozzles to prevent clogging.

Performance Tests: Test printed circuits or patterns for durability and functionality, such as RFID tags or sensors.

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6. Application in Inkjet Printing

Ink Formulation: Optimize the graphene dispersion for specific uses like flexible circuits or antennas.

Printing Trials: Test the ink with an inkjet printer to ensure smooth flow and consistent print quality.

Annealing: If necessary, use low-temperature annealing to enhance conductivity without damaging substrates like paper or plastic.

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Key Advantages of Bead Milling

Scalable Production: Bead mills can produce graphene in large quantities suitable for industrial applications.

High Efficiency: The method ensures excellent exfoliation and dispersion, resulting in high-quality graphene with minimal defects.

Customization: Parameters can be fine-tuned to produce graphene with properties tailored for specific inkjet printing needs.

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By using a bead mill, manufacturers can produce graphene-based inks that are cost-effective, environmentally friendly, and optimized for advanced applications like printed electronics.