Date of Award
Bachelor of Science
Paper Science and Engineering
Dr. Raymond L. Janes
Dr. Brian Scheller
The objective of this thesis is to determine the effects that various pigments and binders have on the coated gloss, print gloss, and delta gloss values. The effects of coat weight and calendering on the glossing response of the sheet will also be determined. Supplemental tests such as Parker Print Surf Roughness, brightness, and opacity will be measured to further evaluate the coating formulations.
A total eight different coating formulations were made using four very common pigments and two latex binders. The four pigments used were #2 clay (100%), calcined clay (15% substitution), delaminated clay (25% substitution), and calcium carbonate (100%). The two latex binders used were styrene butadiene (SBR) and polyvinyl acetate (PVAC). Latex binders were chosen because their gloss response when applied in coatings is better than starch or protein binders. In order to isolate the effect of the pigment and binders a number of variables were held constant or within the same range. The solids levels of all coatings was adjusted to 62%. The binder ratio used was 12% based on dry parts pigment. The Brookfield viscosity was adjusted within the same range using polyacrylate. The printing ink and the print conditions were held constant also. The ink used was a low viscosity water based flexographic ink. A low gloss ink was chosen in order to eliminate the effects of the ink on the print gloss.
When pigments are used alone in coating formulations, their particle size has the most dramatic effect on the gloss response of the sheet. The finer particles create a more optically smooth sheet therefore giving higher gloss values. When binders are introduced into the sheet, the pigment to binder particle interaction also plays a major role.
A coat weight increase of 5 g/m^2 gave an average increase in coated gloss of 10% and gave a 20% increase in calendered gloss. The delaminated clay using the PVAC as the binder showed the highest gloss response due to an increase in coat weight. Calendering the sheet improved all gloss values. The effect was greater for coated gloss than for the print gloss. This was desired because it proves that the gloss of ink did not contribute to the print gloss but that it was the coating structure that affected the gloss response. The effect of pigment and binder type varied depending upon the combination used. The calcined clay gave the highest calendered gloss values which was not expected. However, when these samples were printed they displayed the highest delta gloss. This is due to the large particle size of the calcined clay. High delta gloss values are not desired because they produce a contrast between the image of the coating and the printed image. The pigment-binder interaction played a major role in determining the gloss response. When the PVAC binder was used, the delaminated clay gave the best gloss response with a delta gloss value of near zero (.2). When the SBR was used, the #2 clay gave the best response in gloss response. This was expected because the SBR latex is known for its high gloss response. A more detailed description and interpretation of the results can be found in the results and discussion section.
DeMay, Bob, "The Effect of Various Pigments and Binders on Coated Gloss, Print Gloss, and Delta Gloss" (1996). Paper Engineering Senior Theses. 111.