The Influence of Internal Paper Sizing on Water Base Ink Printability

Rotogravure printing inks containing HAP's (Hazardous Air Pollutants) and VOC's (Volatile Organic Compounds) have long been targeted by the EPA for regulation and control. An alternative is water base inks which can be used as direct substitutes for solvent base inks. Implementation of water base ink technology, however, requires a new balance between ink properties, paper properties, and press conditions. The work presented here addresses the interactions between water base gravure inks and paper substrates having a variable level of hydrophobicity. Uncoated papers were made under controlled conditions on a pilot paper machine at different levels of internal alkaline sizing. They were supercalendered and printed in a pilot-plant rotogravure printing press with water base inks. Except for one case where groundwood pulp was added, all papers were woodfree. Results indicated that there were only small variations in the physical properties of woodfree papers; smoothness and compressibility remained unchanged. Although delta gloss continually increased with sizing, print density remained constant up to a certain sizing level, thereafter decreased with increasing sizing levels. Above the critical level, print smoothness (the area of voids in solid prints) also increased substantially. Micrographs of the solid areas illustrated qualitatively that not only a screening defect exists at high sizing levels, but also the air voids are distorted, indicating uneven substrate coverage. These defects were attributed to poor in-plane wetting and spreading of the water base ink over highly hydrophobic surfaces. The groundwood-containing paper demonstrated significant fiber swelling, very high voids area, and low print density. Some additional comments are being made regarding press runnability and printability.