1、Designation: D7394 13Standard Practice forRheological Characterization of Architectural Coatingsusing Three Rotational Bench Viscometers1This standard is issued under the fixed designation D7394; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers a popular industry protocol for therheological characterization of wate
3、rborne architectural coat-ings using three commonly used rotational bench viscometers.Each viscometer operates in a different shear rate regime fordetermination of coating viscosity at low shear rate, mid shearrate, and at high shear rate respectively as defined herein.General guidelines are provide
4、d for predicting some coatingperformance properties from the viscosity measurementsmade. With appropriate correlations and subsequent modifica-tion of the performance guidelines, this practice has potentialfor characterization of other types of aqueous and non-aqueouscoatings.1.2 The values in commo
5、n viscosity units (Krebs Units, KUand Poise, P) are to be regarded as standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and dete
6、rmine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D562 Test Method for Consistency of Paints MeasuringKrebs Unit (KU) Viscosity Using a Stormer-Type Viscom-eterD869 Test Method for Evaluating Degree of Settling of PaintD1005 Test Method for Me
7、asurement of Dry-Film Thick-ness of Organic Coatings Using MicrometersD1200 Test Method for Viscosity by Ford Viscosity CupD2196 Test Methods for Rheological Properties of Non-Newtonian Materials by Rotational (Brookfield type)ViscometerD2805 Test Method for Hiding Power of Paints by Reflec-tometryD
8、4040 Test Method for Rheological Properties of PastePrinting and Vehicles by the Falling-Rod ViscometerD4062 Test Method for Leveling of Paints by Draw-DownMethodD4287 Test Method for High-Shear Viscosity Using a Cone/Plate ViscometerD4400 Test Method for Sag Resistance of Paints Using aMultinotch A
9、pplicatorD4414 Practice for Measurement of Wet Film Thickness byNotch GagesD4958 Test Method for Comparison of the Brush Drag ofLatex Paints3. Terminology3.1 Definitions:3.1.1 coating rheology, nthe viscosity profile obtained fora fluid coating over a range of shear rates.3.1.2 high-shear viscosity
10、(HSV), nthe viscosity of a fluidcoating at high shear rate (typically measured at 10,000 or12,000 sec-1), and for architectural coatings, it is often referredto as the “ICI” or “brush-drag” viscosity.3.1.3 leveling, nthe ability of a wet coating to flow out toa smooth dry film after application, the
11、reby minimizing oreliminating coating surface irregularities that occur duringbrushing, rolling or spraying (see also Test Method D4062).3.1.4 low-shear viscosity (LSV), nthe viscosity of a coat-ing fluid at low shear rate (typically in the range of 0.001 to1s-1), often referred to as the “leveling
12、viscosity” or inverselyas the “suspension viscosity.”3.1.5 mid-shear thickener effciency (MSTE), nthe weightof active thickener per unit volume of wet coating required togive the target MSV, commonly expressed as lb activethickener/100 gal wet coating (or in g/L units).3.1.6 mid-shear viscosity (MSV
13、), nthe viscosity of acoating fluid at medium shear rate (typically in the range of 10to 1000 s-1), often referred to as the “consistency” or the“mixing viscosity.”1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials, and Applications and is the dire
14、ct responsibility ofSubcommittee D01.24 on Physical Properties of Liquid Paints and Paint Materials.Current edition approved July 1, 2013. Published August 2013. Originallyapproved in 2008. Last previous edition approved in 2008 ad D7394 08. DOI:10.1520/D7394-13.2For referenced ASTM standards, visit
15、 the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100
16、 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.7 newtonian, na rheological term describing a fluidthat maintains constant viscosity over a range of shear rates(see also Test Method D1200 and Test Method D4040).3.1.8 rheometer, nan instrument capable of continuou
17、slymeasuring fluid viscosity over a range of shear rates or shearstresses, often capable of other types of rheologicaldeterminations, and ideally suited for research and well-defined characterization of fluid rheology.3.1.9 rotational viscometer, nan instrument that uses oneor more turning surfaces
18、in contact with a fluid to measure thefluids viscosity, is capable of operating at one or morerotational speeds to provide different shear rates, is typicallylimited to one speed per measurement, is relatively simple tooperate and ideally suited for quality control or routine labdeterminations.3.1.1
19、0 settling, nthe gradual sedimentation of pigment orother disperse phase particles, or both, that may occur duringstorage of a coating (see also Test Method D869).3.1.11 shear rate, nthe change in velocity of a fluid perunit gap between shearing surfaces.3.1.12 suspension, nas defined in this practi
20、ce, a coatingformulations ability to suspend pigment and other dispersephase particles, thereby inhibiting or preventing settling orsyneresis, or both.3.1.13 syneresis, nthe separation of a clear liquid layer atthe top of coating in a container that may occur during storage.3.1.14 thixotropy, na rhe
21、ological term describing a non-newtonian fluid that decreases in viscosity with time at a givenshear rate, and then rebuilds viscosity with time when theshearing stops (see also Test Methods D2196).4. Summary of Practice4.1 This practice involves characterization of architecturalcoating rheology by
22、measuring viscosity with three rotationalbench viscometers to obtain low-shear viscosity (LSV), mid-shear viscosity (MSV) and high-shear viscosity (HSV), respec-tively. LSV is obtained with a Brookfield-type spindle viscom-eter operating at its lowest speed (at either 0.5 or preferably 0.3rpm). The
23、applicable shear rate for this viscometer/speedcombination is in the range of 0.01 to 1 s-1. The MSV orcoating consistency is obtained using an analog or digitalrotational paddle-type viscometer that measures viscosity inKrebs Units (KU). The applicable shear rate for this instrumentis in the range
24、of 10 to 200 s-1for most architectural paints. Thehigh-shear viscosity is obtained using a cone/plate-type vis-cometer with a fixed shear rate of either 10,000 or 12,000 s-1.If coatings are to be characterized without any viscosityadjustments being made, measurements with the three viscom-eters can
25、be conducted in any order. However, if a series ofpaints is being compared where it is desirable to have one ofthe three viscosities a constant, viscosity adjustments may beneeded to achieve that. For example, it is quite common tohave a specification for the Krebs Unit viscosity in architec-tural c
26、oatings. In this case, MSV would be the first viscositymeasurement made, and any coatings out of specificationwould be adjusted (usually with the amount of thickener) toobtain the same or similar Krebs viscosity. With the Krebsviscosity constant, meaningful comparisons between coatingscan then be ma
27、de in the extreme shear rate regimes for LSVand HSV where many coatings properties are affected.5. Significance and Use5.1 A significant feature of this practice is the ability tosurvey coating rheology over a broad range of shear rates withthe same bench viscometers and test protocol that paintform
28、ulators and paint QC analysts routinely use. By using thisprocedure, measurement of the shear rheology of a coating ispossible without using an expensive laboratory rheometer, andperformance predictions can be made based on those measure-ments.5.2 Low-Shear Viscosity (LSV)The determination of low-sh
29、ear viscosity in this practice can be used to predict therelative “in-can” performance of coatings for their ability tosuspend pigment or prevent syneresis, or both. The LSV canalso predict relative performance for leveling and sag resis-tance after application by roll, brush or spray. Fig. 1 shows
30、thepredictive low-shear viscosity relationships for several coat-ings properties.5.3 Mid-Shear Viscosity (MSV)The determination ofMSV (coating consistency) in this practice is often the firstviscosity obtained. This viscosity reflects the coatings resis-tance to flow on mixing, pouring, pumping, or
31、hand stirring.Architectural coatings nearly always have a target specificationfor mid-shear viscosity, which is usually obtained by adjustingthe level of thickener in the coating. Consequently, mid-shearviscosity is ideally a constant for a given series of coatingsbeing tested to provide meaningful
32、comparisons of low-shearand high-shear viscosity. With viscosities at the same KUvalue, MSV can also be used to obtain the relative Mid-ShearThickener Efficiency (MSTE) of different thickeners in thesame coating expressed as lb thickener/100 gal wet coating org thickener/L wet coating.5.4 High-Shear
33、 Viscosity (HSV)High-shear viscosity inthis practice is a measure of the coatings resistance to flow onapplication by brush or roller, which is often referred to asbrush-drag or rolling resistance respectively. This viscosityrelates to the coatings ability to provide one-coat hiding, itsease of appl
34、ication (brushing or rolling resistance), and itsspread rate. Fig. 2 shows high-shear viscosity relationshippredictions for relative coating performance.FIG. 1 Low Shear Viscosity (LSV)D7394 1326. Reagents6.1 Viscosity Standardsoptional, for checking the accu-racy of each of the three viscometers us
35、ed in this practice.7. Apparatus and Equipment7.1 Spatula or Lab Stirreroptional, for mixing coatingsamples prior to viscosity measurements.7.2 Brookfield-Type Viscometerto measure the low-shearviscosity of a coating at the lowest instrument rpm (BrookfieldLVT at 0.3 rpm is standard, LVT at 0.5 rpm
36、is optional).7.3 Paddle-Type Rotational Viscometerdigital or analoginstrument to measure the mid-shear viscosity of the coating inKrebs Units (KU).7.4 Cone/Plate-Type Viscometerto measure the high-shearviscosity of the coating at a fixed shear rate of 10,000 or 12,000s-1, depending on whether the el
37、ectrical system is 50 or 60 Hz.7.5 Thermometer (ASTM 49C or equivalent of 0.1C accu-racy per Test MethodD562 or Test MethodsD2196)to recordand adjust the coating sample temperature.7.6 Leveling Draw-Down Bladeoptional, to determine therelative leveling of coatings for comparison and correlationwith
38、low-shear viscosity measurements.7.7 Sag Baroptional, to determine the sag resistance ofcoatings for comparison and correlation with low-shear viscos-ity measurements.7.8 Paint Brushoptional, for brushing out paints for rela-tive brush drag, wet film thickness, hiding power, and levelingof brush mar
39、ks for comparison and correlation with low-shearand high-shear viscosity measurements.7.9 Paint Rolleroptional, for rolling out paints for relativerolling resistance and for measuring wet film thickness, hidingpower, and leveling of roller tracking marks for comparisonand correlation with low-shear
40、and high-shear viscosity mea-surements.8. Procedure8.1 Background and Testing Protocol:8.1.1 A common practice in many architectural coatingslabs is the examination of coating viscosity in three shear rateregimes using three different rotational bench viscometers: aBrookfield-type spindle viscometer
41、 at low rpm for low-shearviscosity (LSV), a fixed speed paddle-type viscometer formid-shear viscosity (MSV), and a cone/plate-type viscometerfor high-shear viscosity (HSV). This test protocol is describedbriefly in theASTM Paint and Coatings Testing Manual3and inmore detail in the Handbook of Coatin
42、gs Additives.4Althoughcontrolled shear rate and controlled shear stress rheometers doprovide more complete coating rheology profiles, have welldefined shear rates and shear stresses, are often more accuratein their measurements, and can provide other rheologicalinformation such as elastic properties
43、 etc., many routinedecisions about relative coating rheology performance predic-tions are made using the test protocol of this practice.8.1.2 The mid-shear Krebs Unit viscosity is a primaryspecification for nearly all architectural coatings. Consequentlythis is usually the first viscosity measuremen
44、t made. If theKrebs Unit viscosity is not on target, a common practice is toadjust thickener level to bring the coating into the correct KUspecification range. Krebs Unit viscosity specifications forarchitectural coatings can range from about 70 to 120 KU 6 3KU, depending on the type of coating and
45、application. For atypical house paint with a midpoint specification of 100 KUviscosity, the specification range would be 63 %. Since MSVis often a primary specification, a series of coatings beingcompared for rheology will often have the same or similar KUviscosity, and this is actually advantageous
46、 and important formeaningful comparisons of LSV and HSV. The reason for thisis that an increase in MSV for a coating will result in acorresponding increase in its LSV and HSV. If the coatings donot have the same MSV, viscosity comparisons at low and highshear cannot be made on an equal basis.8.1.3 I
47、n some protocols, LSV or HSV can be a primaryspecification for a coating with MSV having secondary prior-ity. In those instances, LSV or HSV are adjusted to constantvalue with thickeners or rheology modifiers, or both, and theother two viscosities are then determined for comparison8.2 Adjustment of
48、the Mid-Shear Rate Krebs Unit Viscosity:8.2.1 A first step based on the preferred test protocoloutlined above in this practice is the determination of the Krebsviscosity (or just KU viscosity) of the coating using a paddle-type analog or digital viscometer that measures viscosity inKrebs Units. Test
49、 Method D562 is the test method recom-mended for this determination. All setup and operationalcriteria should be followed. As some paints are thixotropic, itis a good practice to pre-stir the paint with a spatula or labmixer to break up any structure prior to making a viscositymeasurement. If the mid-shear Krebs viscosity is a specifica-tion or is a fixed value for the paints being tested, the Krebsviscosity of each paint should be measured followed byappropriate thickener adjustments to obtain the same or similarKU before proceeding to obtain LSV or HS
