MECHANISMS OF PRINT GLOSS DEVELOPMENT

In nip printings like offset, print gloss was dependent on coating materials (acrylonitrile groups content and gel content of latex), coating formulation (latex content), coating structure (pore volume and smoothness), printing conditions (speed and linear pressure) and ink conditions (ink volume on plate and tackiness). Those factors affected ink transfer, ink holdout, magnitude of an initial split pattern and penetration rate of the vehicle controlling the ink viscosity. These mechanisms were exemplified by continuous print gloss measurements immediately after printing and by continuous observations with a video microscope. Additionally, three-dimensional shape of dried ink films printed on paper was measured with a confocal laser scanning microscope. It showed that stripes looking white in video images were valleys with gentle slopes on both the sides. It was found using a freeze-drying technique that valleys generated in printing become shallow with time. Printing (threading) direction, MD or CD, also affected print gloss. Anisotropy in ink solvent absorption into a coating somehow due to fiber orientation of the base paper was suggested to cause print gloss anisotropy.