Ink Holdout and Dot Gain When a Stock Changes Grade
Changing stock grades alters micro-porosity and light scattering, shifting ink holdout and dot gain, requiring immediate press curve and ink film adjustments.
Solid Ink Density
Spectral Density
Optical concentration measurement evaluates the pigment thickness deposited on a packaging substrate during lithographic runs. Solid ink density quantifies the physical quantity of colorant absorbed by paper fibres under standard press conditions. Presses check this optical property continuously to prevent dot gain variations across folding carton productions.
Photometers measure light absorption through filters matching cyan, magenta, yellow, or black process pigments. Higher pigment layers absorb more incident light, producing higher numerical readings on densitometers. Converters calibrate these instruments against absolute white standards before evaluating production sheets.
Tolerances remain tight on luxury cosmetic cartons where brand color variation causes immediate rejection by brand owners.
Substrate Interaction
Surface porosity dictates how liquid carriers penetrate folding boxboard before polymerization locks the pigment in place. Uncoated offset papers absorb vehicle fluids deeply, pulling colorants beneath the surface and lowering maximum densitometric values. Coated boards present smooth clay layers that keep pigment films thin and concentrated at the top interface.
Higher pigment retention on coated stocks increases optical values without requiring additional fountain solution adjustments. Press operators must monitor dampening water flow because excessive moisture emulsifies offset lithographic inks and reduces densitometric readings. Paper mills engineer surface sizing to control liquid absorption rates and maintain predictable printability across large production volumes.
Film Thickness
Press operators adjust fountain keys and ink fountain roller speeds to maintain stable layer depths across the printing cylinder. Wet film thickness determines dry color strength once volatile solvents evaporate or vegetable oils oxidize on the board surface. Thin layers produce weak chroma and washed images, whereas excessive deposition causes bleeding and poor intersheet transfer in delivery stacks.
Print inspection systems track these optical targets automatically, pausing high speed rotary presses when values drift outside acceptable process limits. Quality control managers analyze historical densitometric logs to trace color shifts back to plate wear or pigment batch inconsistencies. Proper calibration prevents costly substrate waste during extended packaging production runs.