Modeling coating structure development using a Monte Carlo deposition method Part 2: validation of the model and case study.

Application: A computer model that simulates the development of coating structure is a time-saving and cost-effective way to identify the best pigments and pigment combinations.

In Part 1, we introduced a model based on a Monte Carlo deposition method to simulate coating structure development. In Part 2, we compare fine model predictions with experimental results and with data available from published studies. We also demonstrate how this simulation tool can be useful in designing coatings by presenting a case study.

Depending on the case studied, the simulations lasted from a few seconds to a few hours on a single processor. For packings of mono-sized spheres, the simulation values for porosity and micro-roughness compared favorably with results from other published studies. For mixtures of two pigments with different particle sizes, simulations showed that mixing a small amount of small-sized particles with large-sized particles drastically reduces the pore size, which is also a result reflected in published data. To validate our simulations for polydispersed pigment blends, we coated Mylar with two different coating colors using a bench-scale blade coater. A very good agreement is found between the experiment and the simulations.

In the case study, we wanted to improve print and paper gloss in offset printing. The deposition model predicted an increase in surface micro-roughness with increasing pigment size, which leads to a decrease in paper gloss. TO improve print gloss without impairing paper gloss, we need to increase micro-smoothness without reducing the pore size. Consequently, we narrowed the particle size distribution and kept the average particle size constant to create, in simulation, a new pigment. This "engineered" pigment should give both higher print and paper gloss in offset printing.

Vidal, Zou, and Uesaka are with the Pulp and Paper Research Institute of Canada, 570 St.-Jean Blvd., Pointe-Claire, Quebec, Canada H9R 3J9. Email Vidal at [e-mail]