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Curtain Coating Technology

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Learn more about the curtain coating technique for slot die coating by Mark Miller of Coating Tech Slot Dies including advantages, disadvantages, technical equations to be aware of, and multi-layer coating applications.

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Curtain Coating Technology

  1. 1. CURTAIN COATING TECHNOLOGY
  2. 2. CURTAIN COATING • Advantages o Large gap o Reduced lines and streaks o Increased fluid velocity o Higher line speed • Disadvantages o Air o Vibration o Minimum line speed & flow rate
  3. 3. CURTAIN COATING CURTAIN COATING • Advantages o Large gap (irregular surfaces) Adjustable slot die height from substrate (250 mm)
  4. 4. CURTAIN COATING CURTAIN COATING • Advantages o Reduced lines and streaks (slot die to substrate gap) Air entrainment
  5. 5. CURTAIN COATING U curtain coatingθD CURTAIN COATING • Advantages o Increased fluid velocity (hydrodynamic assist) Hydrodynamic assist of curtain enables high coating speeds (0.5 cm3/s)
  6. 6. CURTAIN COATING CURTAIN COATING • Advantages o Higher line speed (minimum line speed) Weber number We = ρQV/σ We = Weber number ρ = density Q = volumetric flow rate V = impingement velocity σ = surface tension
  7. 7. CURTAIN COATING CURTAIN COATING • Advantages o Multilayer coating (slide die) 24 layers
  8. 8. CURTAIN COATING • Multi-layer coating o 2-3 layers in typical slot die design o Slide die design accommodates more layers o Separate fluid delivery system for each layer o Combined outside the slot exit σtop < σbottom (surface energy stability)
  9. 9. CURTAIN COATING • Multi-layer coating o Challenges  Contact interface  Downstream separation  Viscosity difference between layers  Surface layer differences Invasion of fluid from one layer to another occurs when the layer thickness is less than 1/3 of the coating gap
  10. 10. CURTAIN COATING • Disadvantages o Air o Vibration o Minimum line speed & flow rate
  11. 11. CURTAIN COATING CURTAIN COATING • Disadvantages o Air (entrainment at dynamic wetting line) 3D environmental air disturbances (air shields)
  12. 12. CURTAIN COATING CURTAIN COATING • Disadvantages o Vibration Edge guides (fluid affinity) Material of construction Overcoat and in-bound coating Solvent feed along edge 3D design to carry fluid by mechanical means
  13. 13. CURTAIN COATING Re = ρQ/μ Re = Reynolds number ρ = density Q = volumetric flow rate μ = viscosity CURTAIN COATING • Disadvantages o Minimum line speed & flow rate We = ρQV/σ We = Weber number ρ = density Q = volumetric flow rate V = impingement velocity σ = surface tension U/V U = web speed V = impingement velocity
  14. 14. CURTAIN COATING
  15. 15. CURTAIN COATING
  16. 16. CURTAIN COATING
  17. 17. CURTAIN COATING • Advantages o Large gap o Reduced lines and streaks o Increased fluid velocity o Higher line speed • Disadvantages o Air o Vibration o Minimum line speed & flow rate
  18. 18. CURTAIN COATING • Balance of liquid momentum and surface tension • Uniform pressure across fluid flow between edge guides • If the coating thickness is smaller, then the web velocity has to be higher • Sharp lip edge geometry V = U * h > Vmin = 2σ/ρVcurtain Vcurtain = (2gh)0.5 free fall estimation

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