Screen E-Book (.PDF) - MacDermid Autotype

I’ve come across examples in all sorts offields that have nothing to do with ink designso I suspect that smart ink formulatorshave more possibilities than they mightsuspect.Of course I’m skipping over issues such asensuring particles are small enough not tobe sieved by the mesh, or solving issues ofbalancing evaporation to give quick dryingwithout drying in. These are importantaspects of the ink designer’s art butaren’t directly related to the 1-2-3 theory.However, because 1-2-3 makes it easier forthe ink designer, there is more freedom tosolve these other problems without havingto worry about problems caused bybad printers.In summary, designing the perfect ink issimple. The good printer only asks theink to be highly shear-thinning with rapidrecovery what I call a “High-Low-High” inkand to give the other properties (colour,conductivity, enzymic efficiency…) forwhich the print is intended. The ink doesn’thave to compensate for a high Rz or a thickstencil or an inappropriate mesh and thedesigner doesn’t have to worry about controllingthe (wet) ink deposit because itdoesn’t depend on the ink at all!Right at the start we need to kill a commonmyth about slump. As far as screenprinting goes, it has nothing to do withgravity. Our dots and lines are far too smallto be affected by gravity and your printswill slump just as much upside down. So ifslump is nothing to do with gravity, whatis the cause?It is simply the tendency of your ink to wetthe substrate. If you put a drop of wateronto the substrate it might do a variety ofthings. If the substrate is Teflon then thedrop will just sit there with no slump. If thesubstrate is glass then the water spreadsout, driven by surface tension, till the drophas become very thin. A typical polymersubstrate will be somewhere in betweenwith intermediate slump.The angle the drop makes to the substrateat any time is the ‘contact angle’. You startwith an ‘initial contact angle’ and end upwith the ‘equilibrium contact angle’. Atypical drop on glass might start with a 60°angle then slowly slump down to 0°.Stopping slumpSlump is the common term used to describethe fact that a drop or line of inkstarts off at a certain height/width then“slumps” to give a wider line with lessheight.Contact angle decreasing as the ink slumps30