10 Things You Should Know about Flat-top Dots – Part 8

Week #8. When using flat-top dot photopolymer, you will likely experience faster press set-ups with fewer adjustments required through the press run. How?

1. Because of the flat-top dot structure, ink to plate and impression settings pull up faster and require less artistry by the operator. This is because of the innate ability to absorb some of the inconsistencies in the print station. Printers using flat-top dots report they "even out" the skill level of press operators. Scheduling critical jobs to run on a specific shift or by a particular operator is often overcome with the implementation of FTD.
2. In addition to leveling the playing field between press operators and even less than optimal print stations, the flat-top dot structure also experiences a leveling of mounting tape (stickyback) performance. What this means is that you may see favorable results on more than one area of mounting tape compressibility without necessarily seeing a notable difference in dot gain between some plates.
   • Given the statement above, one may ask what exactly that means to them; and it really depends on where you currently sit on the compressibility scale of your chosen mounting tape. Some choose to move to a more firm/less compressible tape to minimize pinholing in solids and allow the dot structure of the flat-top technology to absorb that level of displacement, therefore minimizing haloing in these fine detailed areas. Others may choose to move to a softer tape to allow the press operator to have even greater impression latitude if pinholing, mottle, and SID are not a challenge.
   • The decision to go to more or less compressible mounting tape can also be greatly affected by the durometer of the flat-top plate material. In general, we see harder plates being paired with mounting tapes on the medium to medium-firm end of the tape spectrum. Whereas medium durometer plates are often to the softer or medium-soft end of the mounting tape spectrum.
3. Flat-top technology also aids in absorbing some inconsistencies in other raw materials such as paper or film thickness, and components affected by TIR (such as anilox, plate cylinder, impression roll/drum, and bearings).
4. The reason this is all possible is quite simply the structure dot or print character. As a conventional digital plates transfers from the plate shoulder to the plate face is experiencing a rounding (radius) effect due to the presence of O2 during the main (face) exposure process. The flat-top plate has a sharp angular transition from the plate shoulder to the plate face; therefore the 1:1 reproduction ratio reference in earlier segments of this series.
   • Focusing only on the photopolymer and eliminating the mounting tape factor, under increased impression the conventional digital plate will displace from the plate face and through the radius and onto the shoulder.
   • Again focusing only on the photopolymer and eliminating the mounting tape factor, under increased impression the flat-top dot plate will displace at the shoulder versus seeing displacement (growth) at the face. The three images below were all a 5% tonal patch. Certainly, the flat-top example to the right is set up for success for its ability to receive ink to the printable surface of the dot(s).