Paint defects are a costly issue, causing unnecessary product waste, rework, and loss of time. Many common paint finish quality issues (leveling, sagging, coverage, gloss, etc.) can be prevented by correcting the paint viscosity during production. Paint manufacturers recognize the need to monitor viscosity during production but making viscosity measurement in the production has been challenging since the viscosity of paints can vary under different conditions such as shear rate, temperature, etc.

RheoStream® FC is an automatic process viscosity analyzer, which can provide viscosity curves of the paints during production at a controlled shear rate(s) and temperature.

Why Should Paint Viscosity Be Controlled?

In the paint industry, process viscosity plays a critical role in determining the coatings’ end-user performance. Many end markets for paints and coatings, ranging from home builders to original equipment manufacturers, and viscosity determine whether a paint needs to be applied using a brush, roller, sprayer, or more high-tech application.

Viscosity in the paint industry is essentially a measure of its thickness, which influences paint’s performance parameters such as coating film build, color match, voids, and chemical resistance. A coating must be stable during storage, easy to apply, and ideally, the final surface finish should be smooth and dip-free. Correct paint viscosity is, therefore, the key to good paint quality. A change in viscosity can indicate solvent loss or other quality problems.

The viscosity of paints can change under different conditions. During processing and application, paints are subjected to a variety of different shear regimes [Read about shear rates]. For example, in the production process, paint is pumped around the plant, subjecting it to moderate to high shear, whereas storage and transportation are low-shear processes. An application can vary from moderate (dipping) to high shear (roller coating, spraying).

In the low shear regions (< 10 [1/s]), paints are expected to have high, solid-like viscosity to prevent phase separation and sedimentation. During production (10 – 1000 [1/s]), the paint is expected to have a medium viscosity such that it is easy for pumping, mixing, or stirring. During application (> 1000 [1/s]), the paint must be thin enough such that it is easy to apply by brushing, rolling, etc.

Common paint defects that may arise due to viscosity include:

  • Sagging
  • Poor Levelling
  • Dripping
  • Sedimentation
  • Poor Coverage
  • Poor flow
Viscosity of a wall paint

Process Challenges For Viscosity Measurements

Measuring viscosity on the factory floor with traditional instruments like flow cups and viscometers is labor-intensive, time-consuming and prone to inaccuracies. Moreover, they provide only single point viscosities, which does not provide the complete picture of paint behavior. A single point measurement is only sufficient if the paint has the same viscosity at all the shear rates occurring during production and application. This is, however, not the case for non-Newtonian, shear thinning liquids such as paints. (See “Why Shear Rate Matters in Process Control”).Therefore, the generation of a viscosity curve that spans the shear rate range of interest can provide the information required to characterize and control product performance.
Image of hand holds paint roller and painting a wall, by Mirsad

Benefits Of Using RheoStream® FC In Production

RheoStream is a process viscosity analyzer that can continuously monitor viscosity in near-real-time during paint production. This enables quality control of the intermediate and/or homogenized paint and ensures quality of the finished product.

Moreover, continuous monitoring of process viscosity can quickly identify and correct sources of error during the production process and could eliminate the need to make decisions based on intermittent “snapshot” data acquired from periodic sampling by laboratory viscometers. If a problem with viscosity is detected early, the number of batches that need to be reworked can be reduced, production capacity can be increased, and any costs towards scraping of products can be reduced.

RheoStream helps to detect any paint batches that are off specification in production by

  • Providing automatic, continuous, near-real time process viscosity measurements
  • Eliminating variations in sample taking and handling
  • Detecting even small changes in viscosity

Additional benefits:

  • High repeatability of viscosity measurements (typical precision < 2%)
  • Controlled temperature for measurements
  • Controlled shear rate(s) for measurements
  • Low maintenance
  • Easy installation
  • Fully automatic cleaning

 

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