Screen frame
The screen frame is the most fundamental element of the screen-printing process. It provides a means for mounting the mesh, must withstand the tension applied to the mesh and the additional forces during printing, remain flat and square, and be light enough for handling.
Once the mesh is tensioned and affixed to the frame, the flatness and stiffness of the frame become critical. A suitable frame will remain flat and square for its service life. Frame distortion causes mesh threads to follow curved directions, leading to mesh distortion at the edges of the screen and reducing the screen's usable, distortion-free area. For high-precision applications in LCD manufacturing and the electronics industry, frames are typically made from solid aluminium alloys. For less demanding applications, tubular frames may be used.
For printing seals on glass plates only about 25-35% of the screen area is typically used for the image.
Mesh
Mesh selection is the result of several compromises. A coarse mesh allows the print material to pass easily, producing thick layers, fast prints, and low resolution. A fine mesh can make it difficult to print bright designs on dark substrates and to pass high-viscosity materials through the screen, but it provides very high resolution. In LCD manufacturing silk meshes are used. High-resolution silk screens have more than 130 meshes per cm, enabling line widths down to 50 µm. Typical printed layer thicknesses are around 10 µm, which in the LCD field is considered a "thick" layer.
The squeegee
- Forcing the print material through the mesh – influenced by mesh opening size and material viscosity.
- Keeping the mesh in contact with the substrate – influenced by screen tension and off‑contact distance.
- Adapting the mesh to the substrate surface – influenced by substrate hardness, roughness and evenness.
- Removing excess print material from the mesh – influences printed layer thickness and image definition.
Squeegees for seal printing are made from a stiff material such as hard polyurethane with hardnesses up to 80 durometer (Shore A). Durometer indicates the blade's rigidity and its resistance to bending during printing. Higher durometers mean greater rigidity; lower durometers allow more flex. Hard squeegees are less forgiving on uneven substrates but are required to withstand high pressures, high speeds and high-viscosity, high-opacity materials on glass plates.
The squeegee angle relative to the mesh defines the amount of material deposited and the required printing forces. Angles of about 15–20° off vertical usually produce an even deposit; the exact setting depends on profile and durometer.
