Screen E-Book (.PDF) - MacDermid Autotype

Moire, causes and cureson top of another region of dots. Skippinghas been discussed at length in Anna andDavid’s section of this eBook.IdentificationUnder a loupe or microscope you seethat the halftone dots are broken up intoseveral smaller dots or the dots are muchsmaller than expected. These small dotsare generally found in the valleys betweenpreviously printed dots.CureGood. For a given ink, there is only oneway to reduce skipping without increasingspreading (or flooding). You most switchto a low EOM, low Rz stencil. As this is verydifficult and expensive to attain with anemulsion, you need to switch to MacDermidAutotype’s Capillex CP or CX which aredesigned specifically to reduce skippingand spreading.Good. Switch to solvent or water-basedUV, both of which give you a lower buildwhich automatically reduces skipping andspreading.3b. Spreading transferSymptomsTricky! It looks like a normal moiré, but itcomes and goes from print to print. Veryhard to pin down unless you know whatyou are looking for.CauseWhen you get spreading (excess ink goingunderneath the stencil because youare printing on top of previous dots), yourstencil is going to ‘print’ that excess ink onto the next print. If you have perfect registrationbetween prints, this will not causea problem. But minor changes in registrationmean that you get extra dots whereyou don’t want them and they appear asa moiré.IdentificationLook at the regular pattern of your realdots. If you have extra dots in betweenthem then this is spreading transfer. Itseems odd to look for dots that shouldn’tbe there, but once you get into the mindset,you find it very easy to track down thistype of pseudo-moiré.CureGood. For a given ink, there is only one wayto reduce spreading without increasingskipping. You most switch to a low EOM,low Rz stencil. As this is very difficult andexpensive to attain with an emulsion, youneed to switch to MacDermid Autotype’sCapillex CP or CX which were designedspecifically to reduce skipping and spreading.Good. Switch to solvent or water-basedUV, both of which give you a lower buildwhich automatically reduces skipping andspreading.102