Screen E-Book (.PDF) - MacDermid Autotype

Solving problemsA quick tip to help with a poor drying setupis to install a de-humidifier in the system.There’s a different sort of drying issue wesee from time to time. If your print is beingdried on a belt going through the oven,the pattern on the belt sometimes showsthrough on the print.The higher thermal conductivity of thebelt means that that part of the print driesfaster, so ink flows from the less dried partto fill in, and the net effect is more ink correspondingto the areas in contact withthe belt.Exposure controlEveryone’s in a hurry and likes to underexpose.It obviously helps with resolutiontoo. But it’s very easy for the current levelof under-exposure to be regarded as beingfull-exposure, so someone under-exposesa bit more … till you get a soft stencil withpoor edge definition and a poor print life.Drifts downwards in levels of under-exposure,coupled with the drift downwards inoutput from the lamps is the single biggestsource of problems we’ve found inthe whole screen-print business!that for prints onto smooth substratesthere can be a lot of static generated whenthe stencil and substrate separate. A fix forthis is to use a rough stencil with lowerstencil/substrate contact. But generallythis reduces print quality. A stencil witha high-frequency micro-roughness (suchas Capillex CP and CX) gives the reducedstatic but without the reduction in printquality.Thick edgesIt’s amazing how many printers try to usea thick stencil to get a thick print. This canwork for narrow features, but then youget other problems such as negative sawtoothingdescribed below. But in general, athick stencil merely gives you a thick edge,simply because the stencil has no influenceon the amount of ink that’s printed afew mesh holes away. As we’ll see in a moment“no influence” hides another problemcaused by thick stencils.78StaticWe’ve already mentioned static in termsof dirt. It can also cause cobwebbing anddendrites (patterns like a bolt of lightning!).Good earthing of the press, preserving amoderately high relative humidity andadding an ionised air flow will all help reducethe static. In addition we’ve foundThis thick stencil will give negative sawtoothing