What causes ink stains?

Ink stains, which manifest as blotchy spots on both the printed and shadowed areas of glass, can significantly diminish the quality of screen-printed images. This issue is prevalent in glass screen printing, and several factors contribute to its occurrence:

Slow Drying of Ink: If the printing speed is not well-matched with the drying rate of the ink, the ink may not dry evenly, leading to the formation of spots.
Thin Ink Layer: A too-thin ink film can result in uneven coverage, making the surface susceptible to blemishes.
High Thixotropy of the Ink: Inks with high Thixotropic properties resist flowing evenly, causing irregular ink distribution and spot formation.
Static Electricity: Static electricity during printing can interfere with ink transfer and result in patchy prints.
Poor Pigment Dispersion: When pigments in the ink are not well dispersed, the polarity of pigment particles can cause them to clump together. This clumping leads to colour spots and uneven printing.
Improvement Methods:

Enhance Ink Flow: Adjust the ink formula to improve its flow properties, ensuring a smoother and more even application.
Use Fast-Drying Solvents: Switching to solvents that dry quickly can help minimize the risk of ink spots forming due to slow drying.
Print with High-Viscosity Ink: Using ink with a higher viscosity can create a more uniform and thicker film, reducing the likelihood of stains.
Increase Wet Film Thickness: A thicker wet ink layer can improve coverage and reduce spot formation.
Select Low-Oil-Absorption Pigments: Opt for inks made with pigments that absorb little oil to minimize pigment clumping and improve dispersion.
Minimize Static Electricity: Take measures to reduce static electricity during printing, such as using anti-static equipment or controlling humidity levels in the printing environment.
Implementing these methods can minimize the likelihood of ink stains, ensuring a higher quality and more consistent printed result on glass.