This licentiate thesis comprises two parallel studies dealing with water-based flexographic inks on PE-coated liquid packaging board. The commercial waterbased inks that were used in both studies vary in type of pigment and acrylatepolymer vehicle, and in pigment/vehicle mixing proportions. One vehicle is solely based on emulsion polymer, another contains solution polymer, and the third is a 50/50 blend of these two. The first study presents results from characterisation of a matrix of these water-based inks with respect to their rheology, surface tension and wetting of PE-coated board. The rheological properties were measured over a wide range of shear rates relevant to various stages in the printing process. All inks represent shear thinning fluids, forming thixotropic structures. The plastic viscosity and yield stress are shown to increase strongly with content of solution polymers (at comparable solids contents). Measurements of static surface tension and drop spreading, on untreated as well as corona treated board, clearly display differences in interfacial properties for the vehicles. An increasing amount of solution polymer give lower surface tension values, while the equilibrium contact angles increase. The validity of a simple model for expressing the ink drop spreading dynamics was tested and could be applied to spreading on treated board. The rheology, surface tension and wetting properties are also shown to depend on the pigment type (cyan or black) in the ink and on the pigment/vehicle mixing proportion. In the second study, the print performance of this matrix of inks on the PE-coated board was evaluated. Changes in the ink formulation are shown to have significant influence on the ink amount transferred to the board and the print quality parameters. The 50/50 intermediate vehicle consistently gave the highest ink amounts, although the highest print density generally was obtained with the vehicle containing most solution polymer. High contents of solution polymer also resulted in more uniform prints and high print gloss. Mottling was most severe with the vehicle containing solely emulsion polymers. The transferred wet ink amount is demonstrated to correlate well with the plastic viscosity and static surface tension of the ink.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-334 |
| Date | January 2004 |
| Creators | Rentzhog, Maria |
| Publisher | KTH, Kemi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Licentiate thesis, comprehensive summary, info:eu-repo/semantics/masterThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | Trita-YTK, 1650-0490 ; 0405 |
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