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Home / News / Industry News / Why Is a Waterborne Coating's Application Poor Even With High Viscosity?
Industry News
Viscosity in a waterborne coating is not better the higher it goes: it needs some structure for storage, yet good flow during application.
If the viscosity change between rest and applied stress is not right, sag resistance, leveling and application feel can suffer. Choosing a thickener with pseudoplastic character offers one way to approach formula adjustment.
In a waterborne coating formula, viscosity affects storage, application and film formation. At rest without enough structure, pigments and fillers may gradually settle, and the coating sags easily on a vertical surface. But if viscosity is too high, brushing may be laborious, roller resistance high or leveling insufficient. Adjustment should not fixate on one viscosity number; it also has to follow how the coating flows under different stress states. Choosing a thickener therefore concerns not only how high the viscosity is but also whether the rheological character meets the real application need.
01
Rest and application differ
In storage the system should stay stable, with less pigment and filler settling and less change in the coating itself. During brushing, rolling or spraying, the coating needs suitable flow. If viscosity stays very high under stress, application resistance rises.
02
Higher viscosity may not level
Raising viscosity only by adding more thickener may change the state at rest but does not necessarily make application smoother. After leaving the brush, roller or spray gun, the coating needs some flow time to spread. With an unsuitable rheological state, insufficient leveling and uneven coverage can appear.
03
Shear state matters too
A coating at rest sees low shear, while stirring and application usually apply stronger shear. If a thickener keeps viscosity high at low shear and lets it drop clearly as shear increases, support at rest and flow during application can both be served.
Polyurethane associative thickeners
A polyurethane associative thickener affects the rheology of a waterborne system through association between molecules. Its thickening behaviour relates to interactions with resin, surface-active substances and other formula components. DH-7216S is of this type, with relatively high viscosity at low shear and strong pseudoplasticity. A coating at rest or low shear can show high viscosity, while under stirring or application shear the viscosity falls as the state changes. This offers a direction for balancing rest support and application flow in waterborne coatings. The final performance still depends on the specific formula: even the same thickener may behave differently with different resins, pigment and filler contents and other additive combinations.
DH-7216S in the formula
TypePolyurethane associative waterborne thickener
AppearanceColorless to milky white viscous liquid
Solids40%±2%
pH6-8
Reference viscosity (25℃)5000-8000
Specific gravity1.02-1.04
The product has some dispersing ability and can help pigment wetting and dispersion in the formula. Its nonionic character makes it less sensitive to pH change, and the data show no obvious effect on film gloss. It suits waterborne coatings of all kinds and binders.
It can be added directly to the coating under stirring, or first diluted with 3-5 times its weight of water. The reference dosage is 0.5%-1% of the total formula, adjusted to the target viscosity, application method and formula composition. In trials, add in gradients, observe viscosity at low shear and at higher shear, and check leveling, sag and application feel, so the result is not judged from a single viscosity reading.
Temperature also affects thickening
Rheological performance of a thickener is influenced by temperature. According to the product data, DH-7216S has higher viscosity at low temperature and lower viscosity at high temperature. The product may also crystallize in a cold environment. The data state that this crystallization does not affect performance, but the product must be heated until the crystals melt completely before it is used in the formula. After winter storage or low-temperature transport, check the product state first; if crystals are found, heat as the product requires and use it only after they have melted, instead of adding crystallized product directly to the coating, which would affect handling and mixing.
Frequently Asked Questions
Why does high viscosity not guarantee good application?
Rest and application have different needs. If viscosity stays high under stress, application resistance rises, and raising viscosity alone may not give sufficient leveling.
What is notable about DH-7216S?
It is a polyurethane associative thickener with relatively high viscosity at low shear and strong pseudoplasticity, with solids of 40%±2% and pH 6-8.
How is it added?
Directly into the coating with stirring, or after dilution with 3-5 times water, at a reference dosage of 0.5%-1% of the total formula.
What if the product has crystallized?
The crystals do not affect performance, but the product must be heated until they melt completely before it goes into the formula.
SummaryThickening a waterborne coating is not just raising viscosity to a number; it must consider structural support at rest and flow during stirring and application. DH-7216S, a polyurethane associative thickener with high low-shear viscosity and strong pseudoplasticity, can be used for rheology adjustment in waterborne coatings and binders. In formula design, test resin type, pigment and filler composition, application method and ambient temperature together to settle a suitable dosage and method of use.
