Tests and Rheometers Available for the Rheological Characterization of Paints and Coatings by Anton Paar

Topics Covered

Background
Rotational Viscometers and Rheometers
Rotational Viscometer and Rheometer Systems Available on The Market
Determining the Viscosity and Rheology of Samples
     Rotational Viscometers
     Oscillatory Viscometers
          Amplitude Sweep
          Frequency Sweep
          The Effect of Temperature
Application of Rheology in Paints and Coatings
Suitable Rheometers from Anton Paar
          RheolabQC Quality Control Rheometer
          Physica MCR Series Rheometers
               Physica MCR 51 Rheometer
               Physica MCR 101 Rheometer
               Physica MCR 301 Rheometer
               Physica MCR 501 Rheometer

Background

Anton Paar GmbH produces high-end measuring and laboratory instruments for industry and research. It is the world leader in the measurement of density, concentration and CO2 and in the field of rheometry. Anton Paar GmbH is owned by the charitable Santner Foundation.

Over 1180 employees at the headquarters in Graz and the thirteen sales subsidiaries worldwide ensure that Anton Paar products live up to their excellent reputation. The core competence of Anton Paar – high -precision production – and close contact to the scientific community form the basis for the quality of Anton Paar's instruments.

Rotational Viscometers and Rheometers

In contrast to rheometers, viscometers provide information on the viscous behavior of the sample. Rheometers determine additional properties such as elasticity, stiffness, and structural regeneration under different conditions (pressure and temperature). Rheometer measuring systems have two parts. These are typically normed cylinders consisting of a measuring cup and measuring bob. Cone/plate or plate/plate measuring systems (ISO 3219 and DIN 53018 and DIN 53019) are also widely used.

Rotational Viscometer and Rheometer Systems Available on The Market

Measuring systems available on the market are grouped as follows:

  • Absolute measuring systems (such as concentric cylinders, cone/plate and plate/plate measuring systems) which have a defined shear gap and provide constant shear conditions. These systems are described in ISO 3219 (1993) and DIN 53019 (Version 2004; previously Version 1976 in DIN 53018).
  • Relative measuring systems (such as vanes, spindles, in the form of disks, pins or balls) which have an ‚infinite’ shear gap and therefore do not provide constant shear conditions. For this reason, the viscosity results given by relative measuring systems are not absolute values.

Determining the Viscosity and Rheology of Samples

Rotational Viscometers

With simple viscometers one or different speeds are manually set in steps and the resulting torque (M) is measured, either in percent or per mille of the maximum. The shear rate ã can be calculated from the speed n. This measurement method is called a controlled shear rate test, abbreviated as CSR. The torque (M) provides the shear stress (ô).

Figure 1. (left) Cylinder measuring system; (middle) Cone/plate measuring system; (right) Plate/plate measuring system

Figure 2. CSR setting

There is a second method for determining the viscosity in which the torque (shear stress) is set and the resulting speed (shear rate) is measured. From these two values the viscosity (ç) is calculated. This method is called a controlled shear stress test, abbreviated as CSS.

Figure 3.CSS setting

Using both measurement methods it is possible to determine individual viscosity values or a complete viscosity curve. The viscosity curve describes the viscosity dependence of the sample in a defined shear load range.

Samples which begin to flow only after a certain amount of load has been applied are said to have a yield point. This can be determined using the two different methods: CSS and CSR. In the CSS method the yield point can be read off as the point at which the ô-axis is crossed. In the CSR method the yield point can be calculated approximately using a mathematic regression model (e.g. Bingham, Casson, Herschel-Bulkley). The CSS mode is the more accurate method as it determines the real point of flow.

Figure 4. Flow curve with and without yield point

Oscillatory Viscometers

In an oscillatory rheometer the moving part of the measuring system oscillates, creating vibrations which are transferred to the sample. This provides information on the viscoelastic behavior of the substance. The oscillation is usually carried out at very low deformations to stay in the elastic range. In contrast to rotational tests, oscillatory tests have the advantage that the samples are not destroyed during testing.

Figure 5. Movement in rotational tests (left figure) and oscillatory tests (right figure)

Amplitude Sweep

An oscillatory test simultaneously determines both the viscous behavior, e.g. described by the loss modulus G", and the elastic behavior, e.g. described by the storage modulus G'. A variety of measuring systems allow both liquids and solids to be measured. This makes it possible to use one single instrument to investigate substances ranging from fluids such as water to cured sealing compounds, resins, and even solid plastics.

Figure 6. Setting for an amplitude sweep

Depending on the type of oscillatory test the frequency, deformation, and temperature can be varied. In an amplitude sweep the amplitude is varied and the frequency kept constant. This test provides information on the limit of the linear-viscoelastic (LVE) range and the structural character of the sample. The following characters are defined: Gel or paste character with G' > G'' and liquid character with G'' > G'. The structural strength of a substance is expressed by the G' value.

Figure 7. Possible result (amplitude sweep)

Frequency Sweep

In a frequency sweep the frequency is varied and the amplitude kept constant. The strain is determined from a prior amplitude sweep test to ensure the measurement is carried out within the LVE range. Measurements at high frequencies represent the short-term behavior of a sample. The long-term behavior (storage stability) is described by measurement data at low frequencies.

Figure 8. Setting for a frequency sweep

Figure 9. Possible result (frequency sweep)

The Effect of Temperature

For temperature tests a constant frequency and constant strain are set. The temperature is changed at a defined heating or cooling rate. Temperature tests can be used to determine the glass transition temperature and melting temperature.

Figure 10. Temperature test on a semicrystalline plastic

Application of Rheology in Paints and Coatings

Which test type is most suitable for my specific application?

Suitable Rheometers from Anton Paar

Anton Paar provides the widest range of rheometers for the rheological characterization of paints and coatings.

RheolabQC Quality Control Rheometer

RheolabQC is a quality control rheometer based on state-of-the-art technologies also used in R&D rheometers. It combines unrivaled performance with easy operation and robust design. From quick single-point checks flow curvea and yield point determinations to complex rheological investigations: RheolabQC sets new standards for carrying out routine rheological tests. This powerful rheometer is an excellent example of a modern measuring instrument utilizing all available technical possibilities to ensure flexible, reliable and simple operation.

Physica MCR Series Rheometers

The MCR rheometers are based on a concept at the cutting edge of technology. The EC motor technique, the low friction bearing and the patented normal force sensor have been optimized over years to satisfy the highest demands of rheologists. Any type or combination of rheological tests, both in rotational and oscillatory mode, are possible with the MCR rheometers. The modularity of the system allows the integration of a wide range of temperature accessories and special modules. The innovative and patented features Toolmaster™ and TruGap™ are breakthroughs in terms of user-friendliness.

Physica MCR 51 Rheometer

Physica MCR 51 rheometer is a robust ball bearing rheometer for quality assurance and production control. Ideal for high viscosity applications where low torque capability is not required.

Physica MCR 101 Rheometer

Physica MCR 101 rheometer is an air bearing rheometer (basic configuration) for quality assurance and product development. The torque range and angle of deflection are ideal for structured materials (pastes, creams, lotions, suspensions, emulsions).

Physica MCR 301 Rheometer

Physica MCR 301 rheometer is an air bearing rheometer for product development and research. The torque range and angular resolution are ideal for all samples from low viscous liquids up to solids.

Physica MCR 501 Rheometer

Physica MCR 501 rheometer is an air bearing, high-end rheometer for research and development. It has the widest torque range for the most demanding rheological measurements on all samples from liquids to solids.

Source: Anton Paar GmbH.

For more information on this source please visit Anton Paar GmbH.

Date Added: Nov 17, 2010 | Updated: Jun 11, 2013
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