BACK-TRAPPING

When wet-trapping one ink over another, back-trapping is when ink on the paper is being lifted-off by a succeeding print unit. Back-trapping results in grainy or splotchy looking solids and sometimes leads to contamination (discoloration) of the ink in the fountain. In four color process printing, back-trapping is usually characterized by low trap numbers (<50). Reducing the tack of the succeeding ink(s), or reversing their print sequence, might correct the problem; but occasionally a more involved solution is called for. Contact Graphic Ink for assistance.