The document discusses the tensioned web over slot die (TWOSD) technique for coating a moving web. It involves the elasto-hydrodynamic interaction between the web tension, line speed, wet coating thickness, wrap angles, lip geometry, and web penetration. Key parameters of TWOSD include the indent distance of the slot die, the span between idler rolls, the web tension over the span, the wet coating thickness, and the line speed. The standard setup has an indent of 0.06-0.09 inches, a span of 2-10 inches, and a tension of 0.3-2.4 PLI. Multiple factors like substrate properties, fluid rheology, and density influence the

1. TENSIONED WEB OVER SLOT DIE

2. TECHNIQUE
• Tensioned Web Over Slot Die (TWOSD)

3. TWOSD
• Elasto-hydrodynamic interaction
o Web tension
o Line speed/flow rate
o Wet coating thickness
o Wrap angles
o Lip geometry
o Web penetration

4. TWOSD
• Pressure in the coating bead > Patm
• P scales with (Line Tension)/(Radius)
• Higher pressure is obtained by increasing line
tension or decreasing radius
• Thinner coating with decreasing radius

5. TWOSD
• Span = distance between idler rolls where TWOSD is occurring
(centerline to centerline)
• Indent = what range can be push the slot die in?
• Tension = over the span of TWOSD coating
• Wet thickness = coat weight for various products
• Speed = line speed for various products
• Angle = is the slot die coming in perpendicular to the web, or at an angle
Surface tension of the substrate (or substrate type)
• Fluid rheology
• Density of the fluids
• Surface energy of the fluids (or type)

6. TWOSD
• Standard setup
o Indent = 0-0.09375 inches
o Span = 4.4375 inches
o Tension = 1.2 PLI

7. TWOSD
• Indent = 0.06-0.09 inches

8. TWOSD
• Span = 2-10 inches
o Increasing span = larger coating window
o Reduced span with higher viscosity fluid

9. TWOSD
• Tension = 0.3-2.4 PLI
o Tension zone isolation important

10. TWOSD
• Line speed
o Reduced line speed = reduced indent
• Lip design
o Shorter
o Curved

11. TWOSD
• TopCoat limitations
o Slot die placement in center of span only
o Pressure (10-30 psi)
 Ribbing = Pressure(Land Length) > Pressure(Land Length-1) > Pressure(Land Length-2)
o Span and Indent are inter-related
o Substrate elasticity

12. TWOSD
• Multi-layer coating
o Option for coating multiple layers thin at high speeds
o Need to keep top layer wet thickness and bottom layer
thickness within parameters
 As top layer wet thickness increases = fluid invasion and
upstream overspill
 As bottom layer wet thickness decreases = fluid invasion,
bead breakup, and presence of feed slot vortex

13. TWOSD
• Elasto-hydrodynamic interaction
o Web tension
o Line speed/flow rate
o Wet coating thickness
o Wrap angles
o Lip geometry
o Web penetration