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Test Fluid Applicator Overview
Unlike dyne test markers, bottled surface tension test fluids require a separate applicator to spread the test liquid over the substrate being evaluated.
The original — and still most widely used — method is to use cotton-tipped applicator swabs, per ASTM Std. D2578 and ISO 8296. This technique is effective, but inconsistency of application pressure, degree of saturation of the swab, or test fluid film thickness will contribute to test-to-test variability. Also, any binders or glue can affect results by being absorbed into the test fluid, which will change its surface tension.
A good alternative for flat surfaces is to use a metering device such as the ACCU DYNE Applicator™, which produces a drawdown 1.5″ in width with a controlled wet film thickness of approximately .0005″. For broader scale evaluations of films and other flat samples, a #3 metering rod, which applies a wet film thickness of about .0003″, is an excellent choice. The latter method will require a precision platform to produce a quality drawdown.