Date of Award

8-2002

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Advisor

Carl P. Tripp

Second Committee Member

Douglas W. Bousfield

Third Committee Member

William J. Desisto

Abstract

Paper coatings are mixtures of pigments, binders and other additives used to improve the optical and printing properties of paper. During application, particle migration may occur resulting in a non-uniform distribution of pigments and binders. This may influence product quality. Raman spectroscopy is a potential tool to characterize coatings in terms of pigment/binder and pigment/pigment distribution. However, there is little work reported on this topic. Various coatings were applied to model substrates, dried and analyzed with Raman spectroscopy. CaC03 pigment and Styrene Butadiene latex binders are easy to detect and monitor in paper coatings when kaolin clays are not present. Raman spectroscopy can detect the subtle differences between Ground Calcium Carbonate (GCC) and Precipitated Calcium Carbonate (PCC). The different morphologies of CaC03, Calcite and Aragonite, can be distinguished and quantified using Raman spectroscopy. Procedures to record and calibrate CaC03 pigment-SB latex binder and Calcite-Aragonite coating color mixtures were developed. Dry blends of the components to record spectra produce good calibration curves. We investigate the particle migration with various particle sizes of pigments and binders. For pigment/binder systems, binder migration depends on the pigment/binder size ratio and not on the absolute concentration of binder in the coating color. Similar results are observed with pigment-pigment systems. A critical size ratio of three is found that determines if particle migration will occur or not. A dissolved polymer in the system is found to reduce migration. Raman spectroscopy can quantify the contribution of the non-uniformity in the spatial composition of the paper coatings to various print defects such as mottle. Large binder/pigment compositions contribute to low density of pigmented ink applied with a contact device. This result must be from low local absorption of ink in that region.

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