Viscosity Determination


ASTM D562
ASTM D2196
BS 3900:A7-1: ISO 2884-1
BS 3900:A7-2: ISO 2884-2
BS EN ISO 2884-2
BS EN ISO 2431: BS 3900:A6
DIN 53211
ASTM D1200
ASTM D4241

 Brookfield Viscometer

 

 

Scope and Field of Application

The viscosity of paints, inks and allied materials is an important property. It affects how easy it is to mix the components of the product during manufacture, how stable it is in storage, how easy it is to apply to a substrate and the manner in which it flows out to form a smooth layer free of defects like runs and brush marks.

Many coatings exhibit non-Newtonian behaviour i.e. the viscosity changes with the shear rate. Thixotropic paints are a common example of non-Newtonian products with the paint having a high viscosity in the can but becoming much more fluid when sheared during application by brush or roller.

Using different viscometers, we can measure the viscosity of samples at low, intermediate and high shear rates. There are no pass/fail criteria defined in the Standards that cover the use of these instruments. This is a matter of agreement between the parties concerned.

The actual standards are copyright-protected documents and we are not able to provide you with copies. If required however, you can easily obtain copies from either the American Society for Testing and Materials, Deutsches Institut für Normung or the British Standards Institution.

Summary of Methods

We can measure viscosity using the six methods described below. In each case the equipment is calibrated using our viscosity oils.

ASTM D562:

This method uses a Stormer viscometer which consist of a paddle-type rotor which is driven (via a cord and pulley arrangement) by a falling weight. The Standard defines the consistency of a paint as the weight required to produce a rotation of 200 revolutions per minute. The standard also includes charts which enables the instrument weight and rotational speed data to be converted to Krebs units (a unit of viscosity measure unique to this instrument).

The range of viscosities that can be measured using this equipment is limited to between about 2 to 50 poise and the method is intended for measurements on DIY and trade paints applied by brush or roller. It is also a convenient method for measuring the viscosity of a sample under low shear conditions.

ASTM D2196

This method uses a Brookfield type rotational viscometer which consists of a variable speed electrically driven shaft on to which can be fitted a number of different spindles. The choice of spindle and rotation speed enables measurements to be carried out in the low to medium shear rate range i.e. 0.1 to 50 sec-1.

The standard is intended for use with non-Newtonian samples and is particularly applicable to thixotropic paints. Methods are described for measuring the viscosity under constant and variable shear conditions.

BS 3900: A7-1: ISO 2884-1

BS 3900: A7-1 and ISO 2884-1 are alternative names for the same method. The method uses a cone-and plate viscometer which, as the name implies, consists of an electrically driven shallow cone the vertex of which touches a rigid temperature-controlled plate. The test liquid fills the narrow gap between the cone and the plate and the torque is measured either electronically or mechanically. The choice of cone geometry and speed or rotation enables a shear rate of between 9,000 and 12,000 sec-1 to be attained and this high shear rate corresponds to that produced during brushing, roller coating and spraying operations.

BS 3900: A7-2: BS EN ISO 2884-2: ISO 2884-2

BS 3900: A7-2, BS EN ISO 2884-2 and ISO 2884-2 are alternative names for the same method. The method uses a Rotothinner viscometer of the type produced by Sheen Instruments (A Division of Hartest Precision Instruments Ltd). A rotating disc is immersed in the sample in a 250 ml container. The container sits on a platform which can rotate but the rotation of which is counteracted by a spring. The greater the viscosity of the sample, the greater the torque acting on the container and the greater the angular rotation of the platform before it is counteracted by the spring. The angular rotation of the platform is read off from a scale which is calibrated in poise. The standard specifies the dimensions of the container and the dimensions and speed of rotation of the disc.

We can use this method to measure viscosities below 15 poise. One advantage of the method is that you can add solvent to a sample under test and measure any change in viscosity. This means it is a good way of determining the amount of solvent needed to thin a paint to a given viscosity. This is exactly the sort of information you need when making paint in a factory.

BS EN ISO 2431: BS 3900: A6

BS EN ISO: 2431 and BS 3900: A6 are alternative names for the same method. It involves the use of flow cups to measure viscosity and the standard includes specifications of four flow cups together with calibration data relating the flow time through each cup to kinematic viscosity. Flow times measured in this way are only reproducible for liquids that are approximately Newtonian but with this limitation in mind, the method is useful for checking that a coating has the correct viscosity prior to spray application.

We can also carry out viscosity determinations using other flow cup standards including DIN 53211, ASTM D1200 and ASTM D4212.

Controlled Stress Rheometry

Using our TA Instruments AR2000 Rheometer and in-house methods, we can provide the following sample characteristics:-

The maximum torque of the rheometer is 200 mN.m with a maximum resolution of 1 nN.m , the resultant measured shear rate is dependant on the geometry selected and the sample viscosity.

The AR2000 rheometer is also capable of acting as a pseudo controlled shear rate instrument, via an internal electronic feed back loop.

Sample Requirements

The volume of sample required for each method is:-

Accreditation

PRA is accredited to ISO 17025 by the United Kingdom Accreditation Service (UKAS) to carry out all the tests listed on this page with the exception of ASTM D562 and ASTM D2196.

We are not accredited to test according to the other methods listed on this page.

Please contact Peter Collins for further details.

 

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