The Effect of a Polymer-Stabilized Latex Cobinder on the Optical and Strength Properties of Pigment Coating Layers

Coated paper with a porous coating layer may have enhanced light-scattering ability and thus favorable optical properties. However, the increased porosity of such a coating layer is likely to decrease the strength of the coated paper, thereby adversely affecting the quality of the paper in the printing and converting processes. In this research, polymer-stabilized (PS) latex was prepared and used as a cobinder for the pigment coating of the paper. The PS latex particles were colloidally stabilized by a 3:1 mixture of starch and polyvinyl alcohol. The influence of the PS latex cobinder on the viscosity, sedimentation, and consolidation of coating colors was investigated. In addition, the effect of the cobinder on the properties of coating layers, namely, their porosity and surface, optical, and tensile properties, was examined. The results revealed that the PS latex cobinder formed microstructures in the coating colors and affected their viscosity. The addition of PS latex also led to enhanced interactions between coating color components, which affected the consolidation of the coating color, resulting in the formation of dried coating layers with greater porosity and improved optical properties (i.e., higher brightness and opacity) relative to coatings without the PS latex cobinder. Furthermore, the addition of PS latex improved the tensile strength of the coating layers, which was attributable to the small size and the polymeric protective shell of the cobinder particles. Thus, these results show that this PS latex cobinder has the potential to be used for the production of high-quality coated paper products.

Effects of the Coating Mixture on the Penetration of Liquids into Paper

The pigment coating of paper is usually performed to enhance the physical properties of paper and its printability. The coating generally makes paper whiter, brighter and more opaque. The properties of the coated paper depend, among others, on the porous structure of the coating developed, which is determined by the pigments, binders and their reactions. The influence of the type and quantity of coating components and ink absorption into the coating layer was studied in this work. Printing ink penetration was measured using a Penetration Dynamic Analyser with an HVL module (High Viscous Liquid). The evenness of liquid penetration into paper was measured using a Penetration Dynamic Analyser with a PEA module (Print Evenness Analyser). Results obtained indicate that all three variables – coating pigment type, latex dose and ink type – may have an equally strong influence on liquid and ink penetration,and thus on print quality.

The influence of pigment proportions and calendering of coated paperboards on dot gain

Dot gain is called Tone Value Increase (TVI). Low dot gain and rounder dot shape are important properties to obtain a good print. Dot gain is a measure of how much extra weight a given percent dot or tone has gained on the final printed substrate by comparison to the actual dot area on a press plate. Dot gain value depends on many factors. The interactions of paper, ink and press conditions are important determinates for a good print. In addition, the pigment coating process and calendering conditions have a significant effect on the printability of paperboards. Pigment coating formulations including mineral pigments, binders and additives improve the gloss, brightness, opacity and smoothness of the paperboards. As a result, print quality of paperboards increase. A uniform paperboard surface is needed to obtain a high quality surface smoothness after the coating process. High surface smoothness improves the uniformity of the dot shape and size. Pigment coating formulation parameters; pigment selection, binder selection and binder level influence print quality. The aims of this study - pigment selection and ratio - are to determine the effect on dot gain in lithography printing. To this aim, base paperboards were coated using five pigment coating formulations which included different combinations of kaolin, calcium carbonate and titanium dioxide pigment with a styrene\n-butyl acrylate copolymer binder using a bar application. After coating, the samples were air-dried overnight under TAPPI conditions. Then, half of the coated-paperboards were calendered. Tone scales from 1 to 100 % were offset printed using black ink on the uncalendered and calenderedcoated paperboards. Then, from the printed tone scale, the tone area values were measured with the Gretagmacbeth Spectrolino spectrophotometer. These values showed that pigment coating improved the surface optical and physical properties of paperboards. After calendering, the roughness values of coated paperboards decreased. In addition, the obtained dot and line sharpness on calendered-coated paperboards were better than on uncalenderedcoated paperboards. However, the dot gain values of calendered-coated paperboards had fewer dot gains than uncalendered-coated paperboards. It was established that the variation of pigment proportions in the coating formulations had no significant effect on dot gain.