Coating Applications - Sprayrhfernan/chem550/pdf/Chem550_Spring_04_7.pdf · CHEM 550 – Formulation of Modern Coatings Spring 2004 Polymers and Coatings Program California Polytechnic

CHEM 550 – Formulation of Modern Coatings Spring 2004

Polymers and Coatings ProgramCalifornia Polytechnic State University

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Coating Application Methods

Air Knife

Blade

Brush

Curtain

Dip

Extrusion

Roll

Slot-Die

Spin

Spray

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Coating Applications Coating Applications -- SpraySpray

Coating Viscosity Decreases

Spray Atomization



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AirAir--Atomized Spray ExampleAtomized Spray Example

Architectural Coating- 20 PVC- 28% NVV- 62 nm Acrylic Latex

Spray Conditions- 25 psi Fluid Pressure- 55 psi Air Pressure

Xing, Glass, and Fernando, JCT, 71, 890 (1999)

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Shear Viscosities of Waterborne Shear Viscosities of Waterborne Latex PaintsLatex Paints

HSV@ 12,000s-1

136 cps

49 cps

8 cps

4 cps



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Shear Rates for Various SubShear Rates for Various Sub--ProcessesProcesses

10-2 10-1 100 10+1 10+2 10+3 10+4 10+5 10+6

log

(Vis

cosi

ty)

log (Shear Rate (s-1))

Settling

WickingMixing

(Slurries) RollCoating

SprayCoating

Sag & Leveling

Brush/RollPick Up

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Xing, Glass, and Fernando, JCT, 71, 890 (1999)



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Shear & Extensional ViscositiesShear & Extensional Viscosities

0

dV

A A -- AreaArea

F F -- ForceForce

Shear Viscosity[Pa s]= Shear Stress

Shear Rate

A A -- AreaArea

F F -- ForceForceV

0

Extensional Viscosity= Extensional Stress

Extension RateFor Simple (Newtonian) Fluids,

Extensional Viscosity (EV) = 3 x Shear Viscosity(SV)For Complex Fluids, EV can be as high as 10000 x SV

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Spray AtomizationSpray AtomizationPrimary Mode of Deformation in Spray is Extensional, not Shear

Coating Ligaments are stretched and disintegrated in to droplets in the spray process



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Extensional Viscosities of Extensional Viscosities of Waterborne Latex PaintsWaterborne Latex Paints

Fernando, Xing and Glass, 25th Int. Conf. Org. Coat., 49 (1999)

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Effect of Polymer ConformationEffect of Polymer ConformationPolymer conformation in solution (hydrodynamic volume) determines the viscosity

Intrinsic Viscosity, [η] = K Mva

Mv - Viscosity average molecular weightK - Huggins Constanta - Mark-Houwink Constant

a = 0.5 at theta(θ) conditions(e.g., polyisobutylene in benzeneat 24oC)a > 0.5 in a good solvent



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Rheology Modifiers in Spray Formulations

OCH2

OR

OHO

HOR

H

H

H

( )n

Hydroxyethyl Cellulose Polyethylene Oxide

( )n

C C OH H

HH

RR--NN--CC--(O(O--CHCH22--CHCH22))xx--[[OO--CC--NN--R”R”--NN--CC--(O(O--CHCH22--CHCH22))xx]]nn--OO--CC--

= O= O

= O= O

= O= O

= O= O

--------

HH HH HH HH

R, R’ = CR, R’ = C1212--CC1818; R” = C; R” = C77--CC3636; x = 90 ; x = 90 -- 455; n = 1455; n = 1--4 4

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Macromolecule in Shear Flow

Stretching

Rotation

Recoil

Debye (1946)

Molecule Undergoes Sinusoidal Expansion and Compression



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Macromolecule in Extensional Flow

Stretching

Coil - Stretch Transitionat Critical Rate (Detected

with Birefringence Measurements

Keller et al.(1980)Opposing Jet MethodPure Extensional Flow

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Optimum FlowBehavior

RheologyFormulation Features

Performance

Structure Property



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Few Key Questions

What are the forces that control coating flow?

What are the characteristic rates of deformation during flow?

What are the relevant modes of deformations?

What is the time frame of flow?

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Roll Coating Application Roll Coating Application Roll Coating (2-roll, forward)

s s -- peripheral speed of rollperipheral speed of rollσ-- surface tensionsurface tensionµµ -- viscosityviscosityg g -- nip clearancenip clearancer r -- roll radiusroll radius

Onset of ribbing (grape-vine) for a Newtonian fluid,

µσ

s gr

=

10 3

3 4

./

µσ

s- Ca, capillary number

Mill and South, J. Fluid Mech., 28(3), 523 (1967)



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Coating Flow in Nip RegionCoating Flow in Nip RegionTotally immersed Partially immersed

Pitts and Greiller, J. Fluid Mech., 11, 22 (1961)

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Rib Formation in Roll CoatingRib Formation in Roll Coating

Fernando, Ph.D. Thesis, NDSU (1986)



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Cavitation

Misting

Application Roll

Substrate

Coating Behavior in Nip RegionCoating Behavior in Nip Region

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Fluid Pressure Profile in Nip RegionFluid Pressure Profile in Nip Region



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HEC Solution Filament Formation at Roll NipHEC Solution Filament Formation at Roll Nip

In typical roll coating operations shear rates are high (103-105s-1).Low viscosities at these shear rates are desirable. High extensionalviscosities are not desirable.

Fernando, Ph.D. Thesis, NDSU (1986)

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Coating Filament and Spatter Coating Filament and Spatter Formation at RollFormation at Roll--NipNip

Glass, JCT, 50, 640&641 (1978)



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Rotational Viscometers



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Extensional ViscometersExtensional Viscometers

Filament Drawing MethodsFilament Drawing Methods

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http://www.ferron-magnetic.co.uk/coatings/airknife.gif

http://www.ixan-diofan.com/images/Air%20knife.jpg

Air Knife Coating Method



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http://aic.stanford.edu/conspec/bpg/annual/v11/bp11-30l.gif

Blade Coating Method

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Curtain & Slot-Die Coating Methods

http://www.ferron-magnetic.co.uk/coatings/curtain2.gifhttp://www.ferron-magnetic.co.uk/coatings/slotdie.htm



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http://www.plastiquarian.com/images/manufact/dip.gifhttp://www.ixan-diofan.com/images/DipIXAN.jpg

Dip Coating Method

http://www.ferron-magnetic.co.uk/coatings/immerse.htm

ppt00 30 30http://www.simplex-products.com/images/PExtruCoat1.gif

Extrusion Coating Method



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ppt00 31 31http://www.ferron-magnetic.co.uk/coatings/revroll.htm

Roll Coating Methods

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http://www.ferron-magnetic.co.uk/coatings/gravure.htm




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http://www.ferron-magnetic.co.uk/coatings/meterrod.htm


Documents

Coating Applications - Sprayrhfernan/chem550/pdf/Chem550_Spring_04_7.pdf · CHEM 550 – Formulation of Modern Coatings Spring 2004 Polymers and Coatings Program California Polytechnic