ASTM_D_7836_-_13.pdf

Designation:D783613Standard Test Methods forMeasurement of Yield Stress of Paints,Inks and RelatedLiquid Materials1This standard is issued under the fixed designation D7836;the number immediately following the designation indicates the year oforiginal adoption or,in the case 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.Scope1.1 These test methods cover three approaches for determin-ing yield stress values of paints,inks and related liquidmaterials using rotational viscometers.The first method uses arotational viscometer with coaxial cylinder,cone/plate,orplate/plate geometry.The second method uses a rheometeroperating in controlled stress mode with similar geometries.The third method uses a viscometer with a vane spindle.1.2 A non-rotational technique,the falling needle viscom-eter(FNV),also can be used to measure yield stress values inpaints,inks and related materials.See Test Methods D5478,Test Method D,Yield Stress Determination for details.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 determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D3925 Practice for Sampling Liquid Paints and RelatedPigmented CoatingsD5478 Test Methods for Viscosity of Materials by a FallingNeedle Viscometer3.Terminology3.1 vane spindle,nspindle in which several(4 to 6)rectangular vanes are attached to the shaft giving the appear-ance of a cross or star when viewed from the end.3.1.1 DiscussionA vane spindle can be immersed in aspecimen without destroying the shear-sensitive structure.3.2 yield stress,nthe critical stress at which a materialgoes from being a deformable solid to showing fluid-likebehavior.3.2.1 DiscussionExamples of such fluids include manypaints and pigment pastes and certain food materials such asketchup.4.Summary of Test Methods4.1 Test Method A uses a viscometer with coaxial cylinder,cone/plate,or plate/plate geometry running a several differentlow rotational speeds.The materials is sheared at each speedand a shear stress value is measured.By plotting shear stressversus shear rate,a dynamic yield stress value is determined byextrapolating the data curve to zero shear rate.“Dynamic”indicates that the material has been allowed to flow and that theyield stress value is mathematically calculated by using abest-fit line through the measured data points.4.2 Test Method B uses a controlled stress rheometer todetermine a yield stress value.This can be done more readilywith cone/plate or plate/plate geometry,but can also beaccomplished with coaxial cylinder geometry.The rheometerapplies a stress ramp to the material,starting at zero andincreasing to a preset stress value above the yield stress of thematerial.As the torque applied to the spindle increases,thespindle will start to move when the yield stress in the materialis exceeded.The stress reading at the onset of spindle rotationis the yield stress value for the material.4.3 Test Method C uses a rotational viscometer or rheometerwith a vane spindle immersed in the material.The vane spindleis rotated slowly at a fixed speed and the torque value isrecorded continuously.The yield stress value is determinedwhen the torque value reaches a maximum.5.Significance and Use5.1 The yield stress of a material is a measure of the amountof force required to initiate movement of that material in apipe,through a pump,or from nozzle.The yield stress alsocharacterizes the ability of the material to maintain particles insuspension.Along with viscosity measurements,yield stressmeasurements have been useful in establishing root causes offlow problems such as excessive orange peel and sagging andin explaining resistance to such problems.After a coating has1These test methods are under the jurisdiction of ASTM Committee D01 onPaint and Related Coatings,Materials,and Applications and are the directresponsibility of Subcommittee D01.24 on Physical Properties of Liquid Paints andPaint Materials.Current edition approved June 1,2013.Published July 2013.DOI:10.1520/D7836-13.2For referenced ASTM standards,visit 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 been applied,flow and leveling tends to be inversely related toyield stress and sag resistance tends to be directly related toyield stress.The ability of an automotive basecoat to keepaluminum and/or mica flakes oriented has been related to yieldstress(direct relationship).6.Apparatus6.1 Multi-speed Rotational Viscometerwit