2 Overview 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
3 1 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
4 1 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
5 1 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
6 Rotational 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
7 Rotational 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
9 all these kinds of stirrers are 1 Simple Test Methodshelix 1helix 2bladeanchorball measuringsystemall these kinds of stirrers arerelativemeasuring systemsstirrer forbuilding materialsstarch stirrer
10 1 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
11 2 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
12 2 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
13 2 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
14 2 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
15 2 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.
16 2 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)
20 2 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
21 2 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.
22 viscosity 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
23 2 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
24 2 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
25 3 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)
26 3 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
27 3 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)
28 atomizer (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
29 3 Behavior after application Printing Process Application examples:- printing inksRequirements:- area printing: without levelling problems- halftone printing: dot sharpness
30 3 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.
31 3 After Coating Step Tests (Rotation): Structure Recovery a) rotation (3 intervals)Preset:three stepslow / high / low shear rateResult:time - dependent viscosity
32 3 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
33 3 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)
34 3 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)
35 3 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''
36 3 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.
37 4 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
38 4 Storage Stability Sedimentation Application examples: - emusion paints- coatings with metallic - effectRequirements:- no demixing - no sedimentation- no syneresis
39 4 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.
40 Controlled 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
41 Storage 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.
42 Frequency 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
43 5 Curing Coatings 5 Curing (powder coatings, UV – coatings) - time - dependent and temperature - dependent melting and curing
45 5 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
46 gel 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'')
47 Comparison 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)
Your consent to our cookies if you continue to use this website.