Scope

This test method covers the determination of particle size distribution of liquid paints and pigmented liquid coatings by Dynamic Image Analysis. This method includes the reporting of particles ≥1 µm in size and up to 300 µm in size.

Significance and Use

1 By following this test method, the particle size, particle size distribution and particle shape of particulates in liquid paint and pigment dispersions can be measured.

2 Particle size, particle size distribution and particle shape have a great effect on the color, opacity and gloss of paints. Reproducing these characteristics is critical to the quality and performance of the paint produced.

3 The dynamic imaging instrument is useful during manufacturing to detect oversize particles as well as the required size distribution of particles in order to provide quality and consistency from batch to batch.

Summary of Test Method

Test specimens are fed through the dynamic imaging instrument which is comprised of a camera sensor and illumi-nation source opposing each other to form a measurement zone where the fluid image is captured and then analyzed for particle size and distribution. The particle size and size distribution values are based on the projected equivalent particle diameter. Shape parameters can be used to identify air bubbles that may be present and eliminate them from the reported data. Other appropriate parameters may be used as well. Likewise for undiluted paints (for example, clear paints), shape parameters can be used to eliminate air bubbles and water droplets that may be present from the reported data. Shape parameter formulations may differ from instrument to instrument.

Apparatus

1 Dynamic Imaging Analyzer, a particle counter, shape and size measuring instrument consisting of a flow through cell, an image capture device, means of illumination and software and readout capabilities. Fig. 1 shows a typical gravity feed system.

2 Paint Shaker—any device manufactured to agitate and mix paints in their containers.

3 Instrument Stand.

4 Reservoir—to contain and mix paint in diluted or undiluted state. Holds up to two litres (2 L) of volume.

5 Agitator—to mix contents of reservoir. Should be capable of mixing paints with viscosities up to 1 kg/m s.

6 Inlet/Outlet Lines w/full flow shut off valves.

7 Drain Line.

8 Metering Pump—a software controlled pump to supply dilution fluid to the sample leaving the reservoir and prior to entering the analyzer. The software signals the metering pump to increase or decrease the diluent flow depending on the particle area per image.

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