What Is The Difference Between Letterpress And Flexographic Printing?

Letterpress printing and flexographic printing belong to the same letterpress system in terms of printing principle, but due to technological iteration, there are significant differences in equipment structure, consumables characteristics and process effects. They can be distinguished from the following five aspects:

Differences in plate structure and hardness
Letterpress printing uses a hard resin plate with a thickness of less than 1mm (hardness of about 90 degrees), and the image and text part has a significant raised height, which is suitable for fine dot printing.
Flexographic printing uses a soft resin plate with a thickness of 1-5mm (hardness of 30-70 degrees). The elasticity of the plate can absorb printing pressure fluctuations and is more suitable for non-planar substrates.
Technical route of ink supply system
Letterpress printing relies on a complex long ink path system composed of an ink fountain, ink roller, and stringing roller. The ink transfer is achieved through multiple roller extrusions, which is prone to ink volume fluctuations.
Flexographic printing uses a short ink path system, which is directly quantitatively supplied by the anilox roller. The amount of ink transferred is accurately controlled by the cell depth (usually 20-40μm), and the stability of the ink layer is improved by more than 30%.
Comparison of physical properties of inks
Relief ink is a high-viscosity paste (viscosity 50-200Pa·s), which requires strong shear force to achieve transfer and dries slowly.
Flexo ink is a low-viscosity liquid (viscosity 10-50Pa·s), which can achieve instant leveling with an anilox roller, and the drying speed of water-based ink can reach 2-3 times that of relief ink.
Differences in printing pressure and effect
The pressure of relief printing is usually 0.15-0.3MPa, which can easily cause deformation of the substrate, and the dot expansion rate can reach 15%-20%.
Flexo printing pressure is controlled at 0.05-0.15MPa, and the dot expansion rate can be controlled within 10%, which is particularly suitable for high-precision printing of 70-150 lines/inch.
Comparison of process applicability
The ink layer thickness of relief printing in solid printing can reach 3-5μm, with high color saturation, but there is a sense of steps in the transition of gradient levels.
Flexographic printing can achieve 0.8-1.5μm thin ink layer printing through 200-300 lines/inch anilox roller, with strong 1%-99% dot reproduction ability, which is particularly suitable for gradient pattern printing on food packaging.