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
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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![](icoLeaf.gif)
Polymer solar cell modules prepared using roll-to-roll
methods:Knife-over-edge coating, slot-die coating and screen
printing![](icoLeaf.gif)
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