Screen printing ink straight from the manufacturer is rarely ready to go. The factory default viscosity runs high. They ship it that way because different jobs need different flow.
You are adjusting for five things: what you are printing, how fine the mesh is, press speed, shop temperature, and the substrate. Each one pushes the ink in a different direction, and they do not always agree.
Fine lines and halftones need the ink to stay put. Keep it thick, dry it slow. If the ink spreads, your halftone turns to sludge. On coarse mesh with heavy coverage, you can go higher on viscosity and crank drying speed. The bigger mesh openings pass thicker ink without clogging.
Speed throws everything off. Run fast and the ink has to clear the screen quick and level before the dryer catches it. Push fluidity up, dry it faster, or the next color smears. Slow printing gives you more slack on both.
Shop temperature catches operators every summer. Past 30°C, the ink thins on its own. Add some body and slow drying so it does not skin in the screen. Cold shop? Thin it down, speed the drying.
The substrate trips people up more than anything. Low surface energy films like PE, PP, and some treated materials fight ink that has higher surface tension. Fish eyes, poor coverage, the usual complaints. A little surfactant or reducer usually fixes it. Absorbent stocks like uncoated paper pull the binder in, leaving pigment sitting loose on top. Run higher fluidity and surface tension here, and give drying more time.
There is no single recipe. The guidelines get you close, but every press and every ink system has its own habits. Operators who run the same stock every day stop using the viscometer and go by feel: how the ink clears the screen, how the edge holds up on the substrate. That instinct develops over time. A viscometer gives you a baseline, and plenty of shops skip even that. If you are dialing in a new ink or a new substrate, measure first, then trust your eyes second.
References
- Wikipedia: Screen Printing: Comprehensive overview of the screen printing process, mesh types, stencil preparation, and ink application fundamentals.
- ISO 2834-3:2008 — Graphic Technology — Screen Printing Inks: International standard specifying laboratory preparation of test prints using screen printing inks, including viscosity and drying measurement methods.
- PrintWiki: Screen Printing: Technical reference covering ink formulation, viscosity measurement methods, and press setup parameters for screen printing applications.
- Flexographic Technical Association (FTA): Industry association providing technical resources on printing processes, ink chemistry, and substrate compatibility for packaging applications.
- ASTM F2252 — Evaluating Ink Adhesion to Flexible Packaging: Standard practice for evaluating ink or coating adhesion to flexible packaging materials using tape testing methods.