Solid- or screen densities?

The CCI color control bars are available as solid bars or screened bars. Whereas the solid bars contain a solid regulating field for each color in every 30 mm wide ink slide zone, the screened version has an 80% screen field (in the case of the 6-color strip) and a 70% screen field (in the case of the 8-color strip) for each color in every zone. This means that with the solid version regulation is done based on each of the measured solid densities. With the screened version, regulation is done based on screen densities.

Solid strips assure even inking over the sheet width with a defined ink film thickness that remains constant right throughout the run. Should print disturbances occur, these are noticeable by solid- and screen densities changes but the defined ink film thickness is held constant by regulation. Regulation proceeds very constantly with only slight fluctuations. This is a universal strip for all applications that are used with large solid areas (packaging printing) or to match solid colors on a nominal value basis to the customer's liking (repro at the printing press).

Research, by FOGRA among others, has meanwhile proven that screened subjects can be regulated much better by using screen fields than by using solid fields. Dot gain changes are caused by temperature fluctuations for example and the resulting changes to the viscosity of the ink, or by ink build-up on the blanket. Dot gain changes seriously impair the appearance of screened subjects and solid measurement cannot detect them.

All in all, printers have to decide already in the prepress which priorities they have and which strip they can best work with. This decision is based on the product requirements.

Solid bars and screened bars can also be used in combination. For example, with a five-color subject consisting of a four process inks and a full solid special color, the four process inks can be regulated according to the screen densities and the special color according to the solid density.