Abstract
The spreading and adhesion behavior of latex is a crucial factor in determining the structure and properties of the low-latex-content pigment coating layer. In spite of its importance, there has been a lack of analytical techniques to describe these characteristics in a coating layer. This study presents novel parameters and techniques for quantitative analysis of the spreading and adhesion behavior of latex binder in a coating layer, which is based on cross-section SEM image analysis. A comprehensive series of model coating layers were prepared to achieve varying extents of latex spreading. This was prepared by using latices with different glass transition temperatures and various drying or dry-sintering conditions. Parameters were developed to determine and quantify the different morphological characteristics of latices in the coating layers, which had advantages over qualitative observation from the SEM images. Developed analytical techniques were applied to reveal correlations between structural properties and the coating end-use properties, which contributed to a better understanding of coating structure development. A transitional change in coating structure was observed in the low latex spreading domain and this largely influenced the end-use properties of coating layers such as the mechanical properties and light-scattering efficiency. Micro-roughness of the coating surface and gloss were positively correlated to the spreading extent of the latex. It was notable that despite low levels of coating shrinkage due to the low latex content, the micro-roughness still changed with latex spreading variations. Quantitative analysis of latex spreading and mechanical properties of the coating layer also enabled us to separate the adhesion behavior of latex binder into physical and chemical aspects. This would propose a strategy for paper manufacturers to optimize their coated paper products.
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