LIMITES OPERACIONAIS DO PROCESSO DE REVESTIMENTO POR CORTINA / OPERABILITY LIMITS OF THE CURTAIN COATING PROCESS

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Curtain coating is one the preferred methods for precision multi-layer coatings at high speeds. Curtain coating belongs to the class of premetered coating methods. Liquid falls as a sheet, or curtain, freely over a considerable height and under the action of gravity before it impinges onto the substrate being coated. Edge guide are needed to maintain at specific width of the falling curtain. Precision curtain coating was originally developed for multi-layer photographic film but its use has expanded to many different applications such as optical films and specialty papers. Some advantages of this process include very high coating speeds, adaptability to a wide range of liquids and flexibility to apply thin liquid layer to irregular surfaces. The operability limits of the process are set by different flow instabilities in the coating bead, such as air entrainment, low speed heels and curtain pulling, and by curtain breakup. The goal of this research is to analyze these operability limits by theory and experiments. The focus is to determine the effect of operating parameters; edge guides design and polymer additives on the coating solution on the bead configuration and liquid curtain breakup. The conservation mass and momentum equations with the boundary conditions were used to describe the flow. The equations were solved all together by Galerkin¿s method with finite element basis functions and non-linear system solved by Newton¿s method. Theoretical results show the bead configuration, including heel formation and curtain pulling as a function of web speed, curtain height and flow rate. Theoretical predictions will also be extended to include viscoelastic behavior of the coating liquid. This results was compared with experimental results to obtain the coating windows for fixed parameters. The visualization results show the critical condition at which a viscoelastic liquid curtain breaks was determined as a function of the rheological properties of the coating liquid. The results show that the viscoelastic properties can affect the force balance in the curtain flow. High extensional viscosity liquids can drastically reduce the minimal flow rate to create more stable curtains.

ASSUNTO(S)

processo de revestimento slot coating elementos finitos finite elements

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