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Paints and varnishes as liquids

Surface science methods to improve wetting, dispersion stability and foam prevention

Thinking of prehistoric paintings, paint is one of the oldest man-made substances. Nowadays, the chemistry of paint is largely understood, so that paint production has moved from being an art to becoming a science.

Partially contributing to this transition are the arising scientific questions focused on good wetting and stable dispersion of pigments. In this area, our surface science instruments provide essential support for the research and development as well as quality control of paints and lacquers all over the world.

Optimizing the spreading behavior in slow and highly dynamic processes

Spreading of liquids is mainly controlled by the liquid’s surface tension. Depending on the way paint or lacquer is applied, either static or dynamic surface tension of the paint or lacquer are more important.

For paints that are applied by paint rollers and brushes, the determination of the static surface tension with our optical instruments or with our tensiometers allows to optimize surfactant addition to ensure good spreading. At the same time, characterizing the surfactant’s efficiency by means of its critical micelle formation concentration (CMC) ensures an economical use.

Spraying and printing are fast processes for which knowledge about the dynamic surface tension is crucial in respect to wetting. Our bubble pressure tensiometers use a wide range of surface formation speeds to characterize the speed of surfactants in solution. This knowledge helps to adjust the liquid’s surface tension to the specific time between drop formation and surface contact.

Evaluating the dispersion’s stability

Whether pigments tend to disperse or form lumps depends on the relationship between surface tension of the liquid and surface energy of the powder. For the latter, Washburn measurements are carried out with our tensiometers to analyze, and to an extent, predict dispersibility. Sedimentation tests with the same instruments evaluate the actual separation behavior of the dispersion.

Quantifying foaming tendencies

Foam formation as a common side effect of surfactant addition is highly undesirable, because it results in a reduced adhesion on the substrate and presents rough and unsightly surfaces. Using our scientific Dynamic Foam Analyzer – DFA100, the foamability and foam stability of paints and lacquers can be quantified in order to optimize the use of antifoaming agents.

KRÜSS Application Reports

AR269: Investigating the foam-inhibiting effect of antifoaming agents in printing lacquers

To avoid the numerous quality problems due to foam, antifoaming agents are added to aqueous printing inks and lacquers. The efficiency of two silicone-based antifoaming agents is investigated and compared using foam height measurements with respect to time.

AR224: Dispersibility predictions - Some practical examples

The free surface energy of differently coated carbon black particles and different plastics is measured. The degree of mixability in the melt is predicted in each case based on calculated adsorption enthalpies and confirmed by stirring tests.

AR207: Applications of Sessile-Drop and Pendant-Drop Techniques in Offset Printing Technology

Fountain solutions and paints as well as the printing and not printing areas of printing plates are characterized in respect to their surface tensions and surface free energies. The article shows how to use these values to evaluate the materials used and control printing quality.

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