Study On Characterization Of Ink Penetration Into Coated Paper And Factors Affecting Ink Penetration

It is determined by ink penetration into coated paper to obtain desired optical density, meanwhile the structure and optical properties of the coating layer has a strong influence on ink penetration. Ink is transferred and sets onto the paper surface in the printing process, which affects printing quality and usage of ink. Cutting is a relative accurate method in the literatures about ink penetration measurement at present. But cutting may bring some damages to paper, which reduces reliability of measurement results. The objective of this experiment was to investigate the influence of pigment, binder, coating process and printing process on ink penetration and characterize the penetration depth through quantitative analysis by confocal laser scanning microscope (CLSM). Binder migration is an important factor which affects ink penetration evenness. Investigation into the characterization of binder migration is qualitative and semiquantitative analysis in the literatures. It was realized to chararterize the three-dimensional analysis of binder distribution and to investigate into the factors that affected binder migration and the effect of binder migration o ink penetration uniformity in this experiment.It was found that shape of pigment affected pigment arrangement by SEM and AFM measurements. Sheet kaolin pigment arranged more tightly and orderly than spindly caco3 pigment. Kaolin pigment covered the coating layer orderly and made coatinglayer more smooth and had fewer pores. Investigation into the three-dimensional ink distribution and penetration was made by optical slices using CLSM. The ink penetration depth of kaolin coating layer was lower and distribution uniformity of kaolin coating layer was better than caco3 coating layer.C element content increased with the increasing drying temperature by the SEM/EDS and AFM measurements. It was found in the phase maps measured by AFM tha carboxylic styrene butadiene latex content increased in tne coating surface. It was abtained that carboxylic styrene butadiene latex content of XY plane in the z-direction was calculated accuratelt and characterization of carboxylic styrene butadiene latex three-dimentional distribution was quantitative. Lower drying temperature made binder migrate to base paper and higher temperature made binder migrate to coating surface, but 130?was appropriate to binder even distribution. Evaporating water decreased and binder migration carried by water evaporation declined with the increasing of solid content. There was more time for water to carry binder in vacuum drying process, which made binder migration degree increase. Infrared drying made temperature increase quickly in coating layer internal, which destroyed hydrogen bonding between water and carboxylic styrene butadiene latex and made binder migration decrease.Pigments particle arranged more orderly and tightly and openness of coating layer decreased with the increasing of binder usage, meanwhile the roughness and ink obsorption declined. Binder migration resulted in unevenness binder distribution, increasing of coating spacing volume, and more middle and big pores, which leaded to bad ink penetration uniformity and dot reproduction. Dot distortion and unclear dot boundary resulted in printing mottle.It could be concluded that the surface print quality could be improved and ink usage decreased by increasing the coating thickness. Calender could increase the smoothness, gloss and closure of coated paper, which resulted in lower porosity, lower amount of ink usage, more even ink absorption and higher print density. It could not resulted in changing of paper printability and ink penetration when coating speed changed between 5m/min and 40m/min. Solid content increasing could lead to lower ink absorption, higher glossy and even ink penetration. Infrared drying made coating layer had higher smoothness and gloss and ink penetration more even, which decreased printing mottle occurring. Hot air drying made ink penetration depth lower, but it leaded to unevenness ink penetration. Vacuum drying made ink penetration deeper and print density decrease.It could be achieved that ink penetration depth, print gloss and print density increased with the increasing of printing pressure. When pressure became 700N, print density changed no longer. When pressure got to 750N, print gloss became decreasing. The contact time between coated paper and rubber declined with the adding of printing speed, which made the decreasing of ink amount transferred to paper, ink penetration depth , print density and print gloss.The common offset ink penrtration depth was deeper and ink distribution uniformity was worse than UV cured ink under the same printing condition. Kaolin and caco3 had no effects on UV cured ink drying, but carboxylic styrene butadiene latex affected UVcured ink drying because drying wavelength of UV cured ink was in the range of ultraviolet absorption. Carboxylic styrene butadiene latex absorbed more ultraviolet radiation and the degree of solidification of UV cured ink decreased with the carboxylic styrene butadiene latex content adding. The UVcured ink penetration depth and distribution did not change with the ultraviolet drying time increasing.