2Overview 1 Simple Test Methods, and Rheometry 2 Flow behavior during the Application3 Behavior after the Application4 Long-term Storage Stability5 Curing of Powder Coatings and UV – Coatings
31 Simple Test Methodstrowel test - high-viscosity fluids: “thick“ - low-viscosity fluids: “thin“ e.g. for dispersionsfinger test - tacky: “long“ - less tacky: “short“ e.g. for paints,offset-printing inks,pigment pastes
41 Simple Test Methods Flow Cups measurement of the flow time of low-viscosity liquidsto determine the kinematic viscosity(weight-dependent viscosity !)Examples: oils, solvent-based coatings,gravure and flexo printing inks
51 Simple Test Methods Falling - rod Viscometers weightFalling - rod Viscometersdetermination of the time of the rodto travel downwardsover a defined distancee.g. for testingoffset-printing inks (highly viscous)and pastesprinting inkfalling rodfalling-rod viscometer, e.g. type Laray
6Rotational Viscometers „Low - shear Viscosity“ (LSV) 1 Simple Test MethodsRotational Viscometersfor testing„Low - shear Viscosity“ (LSV)(which is in fact not really low-shear)preset: rotational speed measurement: torqueUsing the typical spindlesrelativeviscosity valuesare measuredcylindersdiskspinsT-bars
7Rotational Viscometers 1 Simple Test MethodsRotational Viscometersfor testing„Medium – shear Viscosity“ (MSV)originallypreset: force (constant torque),using a freely falling weight (in grams),measurement: rotational speed of the rotational measuring systemnowadays: preset of the speed,measurement of the torqueKrebs spindlesstirrer-like „paddles"relative viscosity values are measured here; typically given inKrebs Units, KU
8„High - shear Viscosity“ (HSV) 1 Simple Test MethodsCone & Plate Viscometersfor testing„High - shear Viscosity“ (HSV)preset: rotational speed measurement: torqueProblem:Friction between cone and plate,since the tip of the cone is not truncated, sitting directly on the bottom plate.Consequence:Friction influencesthe measuring results
9all these kinds of stirrers are 1 Simple Test Methodshelix 1helix 2bladeanchorball measuringsystemall these kinds of stirrers arerelativemeasuring systemsstirrer forbuilding materialsstarch stirrer
101 Rheometry Measuring Systems for Absolute Values Measuring Geometries for rotational and oscillatory rheometeraccording to DIN and ISO 3219Cone & Plate, CPfor liquids;for dispersions only witha limitted particle size(usually < 10 µm)Parallel - Plates, PPuseful for dispersions containingcoarse particles,pastes,offset-printing inks,gel-like materials,polymer meltsConcentric Cylinders, CCfor low-viscosity liquids,solvent-borne coatings
112 Application (flow behavior) Flow behavior during the application- Application behavior in the flowing state when stirring, painting, brushing, rolling, spraying when pumping, dosing, blading, flatstream application, dip coating, pouring,using roboters or high-rotational disks or bellsTest method: Flow curves, at medium and high shear rates (rotation)Requirements:- ability to brushlimited coating forceno spattersroller resistance
122 Application (flow behavior) Coating, Painting, Brushing Application Examplebrush velocity(v = 0.5 m/s)wet layer thickness(h = 200 µm)calculation of the shear rate:Brushing, Painting at medium and high shear ratesbetween 100 and 10,000 s-1
132 Application (flow behavior) Industrial Spray Processes Application examples :Automotive coatings - spray robotershigh-rotational atomizers, electrostatically supportedRequirements:- ability to pump- ability to sprayQuelle: Fotos vom Daimler-Museum, Stuttgart
142 Application (flow behavior) Spraying of Automotive Coatings a) Plastisols: seam sealing and under-body sealing b) Coatings: dip coating, filler, base coat, clear coat c) Waxes: cavity conservationcar body degreasing & phosphatizing electro dip coatingseam sealing underbody sprayingfiller base coat and clear coat cavity conservationSpraying, Coating at high shear rates of 1000 to 10,000 s-1
152 Application (flow behavior) Shear Rate Range ProcessShear Rates (s-1)sedimentation< to 0.01surface levelling0.01 to 0.1sagging0.01 to 1dip coating1 to 100pipe flow, pumping, filling into containers1 to 10,000coating, painting, brushing100 to 10,000spraying1000 to 10,000(high - speed) coating, blade coating100,000 to 1 mio.
162 Application (flow behavior) Overview: Flow & Viscosity Curves flow curvesviscosity curvesyield point1 ideally viscous (Newtonian) without a yield point2 shear-thinning (pseudoplastic) having a yield point3 shear-thickening (dilatant)
202 Application (flow behavior) Shear-Thinning Behavior material at rest: under shear: high viscosity decrease in viscositysuspensionwithneedle-shapedorplatelet-shaped particles(e.g. flakes inmetallic-effectautomotivecoatings)The particles are The particles are suspended randomly orientated in (if there are no flow direction. interaction forces).consequence: shear - thinning flow behavior, decreasing viscosity
212 Application (flow behavior) Effect of rheological additives (1) Example: comparison of flow behavior of a water-based dispersion withadditive 1, a „gellant“ e.g. clayadditive 2, a „viscosifier“ e.g. an associative thickener12flow curves on a linear scaleflow curves on a logarithmic scale21lg 1with yield point2lgSummary: The gellant shows is effective especially in the low-shear range (or at rest, resp.), and the viscosifier in the high-shear range.
22viscosity measurement 2 Application (flow behavior)Effect of rheological additives (2) coating processes shear - thinningflow behaviorSummary:A single - pointviscosity measurementis not sufficient. Brookfield Krebs -Stormerlg flow cups viscosityCoating 1 Coating 2shear ratelglow - shear range high - shear range stirring, painting, rolling, spatters (?) spray coating
232 Application (flow Behavior) Effect of Rheobogical Additives (3) Different rheological additives as thickeners(example: water-based coatings)(1) silica (clay, inorganic gellant(2) cellulose derivative, polymer solution(3a) unmodifiíed polymer dispersion (3b) polymer dispersion with an associative thickener (bar length: 100 nm = 0.1 µm)(1)(2)right side: when shearedleft side: at rest(3a)(3b)For polymer dispersions: lower viscosity even though the higher molar mass of the polymer
242 Application (flow behavior) Effect of Rheological Additives (4) Viscosity functions of pigmented water-based coatingscontaining different rheological additivesas thickeners, in principle:(1) silica (clay), inorganic gellant(2) cellulose derivative, polymer solution(3a) unmodifiíed polymer dispersion (3b) polymer dispersion with an associative thickener
253 Behavior after application 3 Behavior after the application- levelling, gloss, de-aeration- sagging, wet layer thickness, edge coverstructure recovery, time-dependent „thixotropic behavior“Test method: step test, low – high – low shear (rotation or oscillation)
263 Behavior after application Levelling and Sagging Application examples:- brush coatings - spray coatingsRequirements: - Levelling without brush marks or other flow defects- controlled sagging- desired layer thickness
273 Behavior after application Levelling and Sagging Levelling, Brush Marks, Wet-layer Thickness, Sagging Example: Brush Paintsat very low shear rates between 0.01 and 1 s-1 (or at rest, respectively)
28atomizer (bell), electrostatically 3 Behavior after applicationLevelling and SaggingAutomotive Coating:High-rotationalatomizer (bell), electrostaticallysupportedspray processExample forsurface treatment of cars:1 car body mould metal sheet2 kathodic dipping process, anti-corrosion protection3 functional layer4 water-base coat5 clear coatspray coatingproblem:sag controlQuelle: Fotos vom Daimler-Museum, Stuttgart
293 Behavior after application Printing Process Application examples:- printing inksRequirements:- area printing: without levelling problems- halftone printing: dot sharpness
303 Behavior after application Shear Rate Range ProcessShear Rates (s-1)sedimentation< to 0.01surface levelling0.01 to 0.1sagging0.01 to 1dip coating1 to 100pipe flow, pumping, filling into containers1 to 10,000coating, painting, brushing100 to 10,000spraying1000 to 10,000(high - speed) coating, blade coating100,000 to 1 mio.
313 After Coating Step Tests (Rotation): Structure Recovery a) rotation (3 intervals)Preset:three stepslow / high / low shear rateResult:time - dependent viscosity
323 After Coating Step Tests (Rotation): Structure Recovery Comparison of two Formulations of Coatings : Step Test with 3 Intervals100= 0.1 s-1= 0.1 s-1Structure recovery is faster with the „gellant“- less sagging,- high wet-layer thickness,- but maybe poor levelingPas10lg h structure recoveryStructure recovery is slowerwith the „thickener“- good leveling,- but maybe too much sagging1= 100 s-10.1100200300400500600700stime t
333 After Coating Step Tests (Oscillation): Structure Recovery b) oscillation (3 intervals)Preset: three steps low / high / low strain amplitudeResult: the two time-dependent functions ofG'' (viscous) and G' (elastic behavior)
343 After Coating Step Tests (O-R-O): Structure Recovery Step test with 3 intervals, as oscillation / rotation / oscillation (measuring „thixotropic behavior“)preset:1 low-shear conditions (strain in the LVE-range, oscillation)2 high-shear conditions (rotation)3 low-shear conditions (strain in the LVE-range, oscillation)measuring result:1 state of rest2 structure decomposition3 structure regeneration2nd test interval: liquid, at high shear rates1st & 3rd test interval: G‘ > G‘‘ („gel-like structure“ at rest)
353 After Coating Step Tests (O-R-O): Structure Recovery Comparison: 2 Spray Coatings, Step Tests in Oscillation / Rotation / Oscillationtime t0.010.1110Palg G'lg G''100200300500600s crossover G‘ = G‘‘g = 0.2%= 15,000 s-1Structure recoveryliquid,as long as G‘‘ > G‘for leveling2) „gel - like“,when G‘ > G‘‘sagging is stoppedAnalysis:Time point ofcrossoverG‘ = G‘‘can be optimizedby rheologicaladditives.Spritzlack 3 (mit Additiv B)G'G''Spritzlack 2 (mit Additiv A)G'G''Spritzlack 1 (ohne Additiv)G'G''
363 After Coating Step Tests: Structure Recovery a) rotation (3 intervals)result: time-dependent viscosity (here, the viscous behavior is measured only !)b) oscillation (3 intervals)result: two time-dependent functions G'' (viscous) and G' (elastic)here, the whole viscoelastic behavior is measured.
374 Storage Stability 4 Long-term storage stability - settling (sedimentation), flotationsyneresis („blooding“), demixingappearance after a time of rest („consistency“)transport stabilitygelation effects, fluidisation Test method: frequency sweep (oscillation), low frequencies
384 Storage Stability Sedimentation Application examples: - emusion paints- coatings with metallic - effectRequirements:- no demixing - no sedimentation- no syneresis
394 Storage Stability Shear Rate Range Process Shear Rates (s-1) sedimentation< to 0.01surface levelling0.01 to 0.1sagging0.01 to 1dip coating1 to 100pipe flow, pumping, filling into containers1 to 10,000coating, painting, brushing100 to 10,000spraying1000 to 10,000(high - speed) coating, blade coating100,000 to 1 mio.
40Controlled stress rotational tests: 4 Storage StabilitySimple Method: Yield PointControlled stress rotational tests:Flow Curves on alinear scaleYield Point as a limiting value of the shear stress2Break of the structure - at - rest.Super - structure by a chemical - physical network via interactive forces.1ty1 without a yield point2 having a yield point y
41Storage Stability Frequency Sweep: Long-term Behavior Preset: constant amplitude, shear strain or shear stress (within the LVE - range) and variable frequencyPrecondition:First of all, the LVE - range has to be checked by an amplitude sweep.
42Frequency Sweep: Long-term Behavior 4 Storage StabilityFrequency Sweep: Long-term BehaviorComparison of two Coatings: Dispersion Stability0.0010.110Pa-3-2-112rad/sG' > G''1lg G'lg G''Long - term storage stability:Evaluation at a low frequency G' > G'' hence „gel - like“, stable dispersion (Top Coat).G'' > G' hence „liquid - like“,unstable dispersion (Primer).G'' > G'0.01g = 1 % T = +23°Cangular frequency lg
435 Curing Coatings 5 Curing (powder coatings, UV – coatings) - time - dependent and temperature - dependent melting and curing
455 Curing Coatings Rotational Tests gel formation and curing preset: constant shear conditions (shear rate or shear stress) result: viscosity / temperature curve showing a viscosity minimum
46gel formation, hardening or curing process 5 Curing CoatingsOscillatory Testsgel formation, hardening or curing processpreset: constant shear conditions (amplitude and frequency)results: temperature-dependent G' and G'' curvesTm melting temperature (when G' = G'')TCR temperature at the onset of the hardening process,gel formation, curing or chemical reactionTSG sol /gel transition (when again G' = G'')
47Comparison of two Powder Coatings 5 Curing CoatingsOscillatory TestsComparison of two Powder Coatings1023456PaG'G''20406080100120140160180200°CT3004005006007008001,000stimetPowder Coat 1Powder Coat 2g = 0.1 % ω = 10 rad/s preset: T = T(t)