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Slot coating

  Extrusion coating
  Curtain coating
  Slide coating
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   
   

   

   
 

 
 

The Slot Die Group

This group includes several methods that use a similar geometry "slot" die from which the coating transfer flow bridging to the web issues directly from the exit of the die manifold's slot.

Slot-Bead Coating (a.k.a. "slot coating", "die coating")

Possibly the most commonly applied liquid film coating method.
Process Features:
tight die lip-to-web clearance (50 µm - to - 1000 µm)
small 2-D transfer flow ("coating bead") stabilized by viscous and/or capillary interaction with die lip surfaces and moving web
coating zone geometry has strong influence on operating latitude and can influence attainable coating uniformity
applied low-level vacuum extends operating window under certain conditions

Commercial Features: 
extensive range of industrially-important coating solutions and suspensions
wide range of coating thicknesses (typically 10 µm - to - 500 µm).
frugal productions of both small and large volumes because of wide operating window, minimal edge waste, efficient starts and stops
pattern coatings (stripe, "patch") with specialized slot-bead coating systems

Applications
Slot bead coating is extensively used for coating suspensions (slurries, emulsions) and/or "dilute" polymer solutions (i.e., where viscoelasticity effects are not significant).
Some application examples:
PSA tapes, labels and sheets (also including Si release films) that are used in a variety of industries such as electronics, packaging, construction, and medical
medical/pharmaceutical - transdermal drug delivery patches, blood testing strips
electronics - flexible printed wiring boards, battery electrodes, ceramic capacitors
graphic/display films including LCD color filters
packaging including barrier layers of various functions (grease, moisture, oxygen, odor) construction/automotive including films with protective coatings (e.g., "hardcoat")

Extrusion Coating

Process features:
substantial clearance (up to 100 X the final coated thickness) with elongated bead or liquid "bridge" stabilized by viscosity
can coat higher viscosity liquids that may also exhibit substantial elasticity (e.g. polymer melts, "concentrated" polymer solutions)
negligible, avoided or inconsequential liquid interaction with die lips  

Applications:
polymer melt sheet casting
hot melt adhesive coating
membrane casting (polymer solution)
hot wax coating for packaging
casting of flexible polymer belts and sheets

Tensioned-Web Slot Coating

Process Features:
die positioned so that lips intersect nominal web path in a span (no immediate coating roll present) transfer bead essentially a lubrication flow between moving tensioned-web and die lips achieving thinly-coated layer and preventing direct lip-web contact
extremely thin coatings (down to 1 µm) at commercially useful speed and precision
operating window dependent upon lip geometry and also critically sensitive to web characteristics and dynamics (e.g., wrap angle, tension, and web stiffness)
coating uniformity critically dependent on uniformity of web characteristics and dynamics

Applications:
TWSC is employed where extremely thin coatings are required; i.e., thinner than possible with acceptable operability and/or uniformity from slot-bead coating.
magnetic media (magnetic tape and cards)
thin barrier layers
subbing layers for other functional coatings

New UV curing systems for automotive applications
Polymer solar cell modules prepared using roll-to-roll methods:Knife-over-edge coating, slot-die coating and screen printing


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