In screen printing, the squeegee plays a crucial role in transferring ink uniformly and quantitatively through the mesh holes onto the substrate. Factors affecting the quality of screen printing include the angle between the squeegee and the screen, pressure, squeegee speed, blade shape, mesh tension, ink properties, and substrate characteristics. The angle of the squeegee affects the flow rate of the ink; a smaller angle results in more ink flow.
Factors Influencing Squeegee Selection
- Mesh Tension
- The screen must have a certain level of tension, which is limited by the material of the mesh. For example, nylon has a tension of 8-10 kg/cm², polyester 8-10 kg/cm², and stainless steel 10-13 kg/cm². For screens with high tension, a harder squeegee is suitable, while a softer squeegee is needed for looser screens to ensure proper ink flow.
- Ink Properties
- The pH level of the ink determines the type of squeegee to use. The squeegee should be resistant to the ink's corrosiveness. The length, thickness, and hardness of the squeegee should be chosen based on the ink's viscosity, fineness, and hardness.
- Substrate Characteristics
- For hard or uneven surfaces, a softer squeegee is recommended, while a harder one is suitable for smoother surfaces.
- Printing Requirements
- If a large amount of ink needs to be transferred, a softer squeegee is preferable.
- 5.Printing Pressure
- High printing pressure is not suitable for very soft squeegees, as it would result in poor printing quality due to excessive contact between the screen and the substrate.
Types of Squeegees:
Rubber Squeegees: These are commonly used due to their low cost. Their solvent resistance is directly proportional to their hardness.
Polyurethane Squeegees: These offer high strength, wear resistance, and resistance to mineral oils and aliphatic solvents. They also have good ozone, low-temperature, and radiation resistance.
Hardness Index for Common Squeegees:
45°-65°: Soft squeegees are suitable for low mesh count screens, low-viscosity inks, and irregular surfaces.
70°-75°: Medium-hardness squeegees are suitable for various mesh counts, inks, and print products.80°-85°: Hard squeegees are suitable for various mesh counts.
The selection of the right squeegee is crucial for achieving optimal screen printing results. Experience in screen printing must be accumulated through long-term practice. Future discussions will focus on topics like screen printing techniques and equipment, photopolymer plate-making, color halftone screen printing, common faults in plate-making, and quality issues in screen printing.