(635e) Integrated Material-Process-Product Analysis of Polymeric Coating Realization: A Multiscale Modeling Approach

Coating product quality, energy/material efficiency and environmental impact have been primary concerns in polymeric coating manufacturing systems. This is especially true for the automotive coating industry. In plants, these concerns are addressed through improving process control and post-process product quality inspection. More recent efforts include methodological development for integrated product and process analysis and control (e.g., Li et al., 2006; Xiao et al., 2006a,b, 2007). It is found, however, that a certain type of quality problems cannot be eliminated since coating material design related issues are not taken into account in the integrated process and product analysis. On the other hand, the current material development approaches do not take real material application conditions into account (Hegedus, 2004; Nobel et al., 2007). Thus, the material design and the material application are basically isolated activities, which is considered a main reason for ineffectiveness in solving certain types of product quality problems.

In this work, a generic Integrated Material-Process-Product (IMPP) analysis framework based on multiscale modeling is introduced for improving coating realization. In this framework, the principal components are presented as the following four successive steps: (1) to identify interrelationships among material formulation, application processes, product and process performances, (2) to identify model needs and determine scale-sensitive material-process-product variables, (3) to develop necessary models at each scale of length and time and a multiscale information utilization methodology, and (4) to identify opportunities for improving coating realization based on the multiscale models and simulations. The integrated analysis approach can greatly facilitate paint material design and effectively reduce the cycle time of coating product development. It is also worthwhile to point out that the IMPP analysis framework and the multiscale modeling methodology developed in this work are generic and have the potential for contributions well beyond the specific application demonstrated here.

The proposed framework has been successfully applied to the analysis of automotive clearcoat realization through oven curing. Three sets of multiscale models and one macro-micro integration method are developed. The macroscopic CFD model set consists of an air flow model, a radiation model and a panel heating model, which describes the dynamic curing conditions in the oven. The microscopic crosslinked network structure is constructed through Monte Carlo simulation with an extensive use of multiscale material information. Process performance models quantify oven energy consumption and VOC emissions, and a coating quality model correlates network structure parameters (e.g., effective crosslink density) with the final coating properties (i.e., the solvent resistance, intercoat adhesion and scratch resistance). The information passed from the macroscopic model into the Monte Carlo code is generated through a macro-micro integration method.

The multiscale model based simulation has revealed that under the same curing condition (i.e., curing temperature profile), decreasing the initial resin molecular weight leads to a decrease of the final effective crosslink density and thus a decrease of the coating scratch resistance. It means that a lower-molecular-weight resin requires a higher curing temperature or longer curing time. Consequently, decreasing the resin molecular weight consumes more energy in curing, although the amount of emission will be reduced. It is also revealed by the simulation that the coating quality uniformity throughout the vehicle body can be improved through changing curing conditions (i.e., the direction of the air sprayed from the nozzles). These insightful guidelines for improving system performances can be best obtained when an integrated material-process-product approach as developed in this work is utilized.

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