sagging1

Home Sagging of a Film as Function of Viscosity and Time
Flow of a coating film after application is an important criteria for the appearance of a coating. Reduction in solvent content (VOC) such as in high solids and water-borne coatings has required to adopt to use of rheology control agents to permit flow and leveling without excessive sagging of the paint film during drying. The sagging speed of a Newtonian liquid can be estimated using as input film thickness, density of the film, viscosity and acceleration due to gravity. Sagging is effected in a coating formulation by the pigmentation, solvent choice, resin design, crosslinker and catalyst.
Enter data	Units	Conversion		Sag equation
Gravity acceleration (g)			cm/s²	υ =	pgχ²
Density of coating film (p)			g/cm³	υ =	^2μ
Film thickness (χ)			cm	υ = speed cm/sec
Delta Film thickness			cm	p = density g/cm³
Viscosity of film (ľ)			Poise	g = acceleration gravity cm/sec²
Delta Viscosity			Poise	χ= film thickness, cm
Sagging time			sec	ľ = Poise
Results
Film thickness, cm

	Sagging, cm












Sagging, %	Sagging/Film thickness, %











Paint Testing Manual: Physical and Chemical Examination of Paints, Varnishes, Lacquers, and Colors - STP 500, Gardner Sward, American Society for Testing & Materials, Pub. Date: January 1973, ISBN-13: 9780803100992