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Poor substrate wetting can turn an otherwise stable coating or ink formulation into a production problem. The liquid may pull away from parts of the surface, form beads, leave uncovered edges, or develop circular defects after application. These problems affect appearance, adhesion, print definition, and production consistency.
Effective troubleshooting requires more than adding a larger amount of surfactant. Formulators must examine the surface energy of the substrate, coating surface tension, contamination, application speed, defoamer compatibility, and the type and dosage of the wetting additive.
A liquid coating must spread across the substrate before it can form a continuous film. When the coating's surface tension is too high relative to the surface energy of the substrate, the liquid tends to contract instead of spreading evenly. This may produce a high contact angle, incomplete coverage, edge pullback, or cratering.
Low-surface-energy substrates are particularly difficult to coat. Examples may include certain plastics, release-contaminated metals, silicone-contaminated surfaces, and previously coated materials.
Poor wetting may also be caused by:
Oil, grease, dust, wax, or silicone contamination
Inadequate substrate cleaning or pretreatment
Variations between substrate batches
Excessive coating viscosity
Fast application with insufficient dynamic wetting
Incompatible defoamers or leveling additives
Incorrect drying or curing conditions
Contamination introduced during mixing or spraying
The first step should therefore be identifying whether the defect comes from the substrate, formulation, application process, or a combination of these factors.
Inadequate wetting does not always appear in the same form.
A coating that pulls away from a small contaminated area may create a crater or fish-eye. Poor general spreading may appear as uneven coverage, beading, frame-like edges, or reduced adhesion. In printing inks, poor wetting may cause missing dots, irregular edges, color variation, or incomplete transfer.
Craters are often associated with local surface-tension differences. A low-surface-tension contaminant can disturb the surrounding wet film and cause it to withdraw from the affected area. BYK identifies contamination from the environment, substrate, or coating itself as possible sources of such defects.
Before adjusting the formulation, record:
Defect size and shape
Location on the coated part
Whether defects appear immediately or during drying
Whether they occur on every substrate
Application method and line speed
Recent changes in raw materials
Cleaning and pretreatment conditions
This information helps distinguish poor overall wetting from localized contamination.
A substrate wetting additive reduces the surface tension of the liquid formulation so that it can spread more readily across difficult surfaces. The resulting film is less likely to retract from edges or small surface disturbances.
A suitable additive may improve:
Initial spreading
Coverage of low-energy substrates
Flow and leveling
Edge coverage
Anti-crater performance
Application consistency
Appearance of the cured film
TEGO Wet 270 is a highly active wetting additive developed for crater prevention and flow promotion. Evonik lists it as suitable for waterborne, solventborne, and radiation-curing coatings.
Its broad applicability does not mean the same dosage or addition method will work in every formulation. Binder type, solvent composition, pigments, defoamers, viscosity, film thickness, and application speed can all influence the result.
Waterborne coatings often require particular attention to substrate wetting because water has relatively high surface tension. Formulators may use surfactants and surface additives to improve spreading on plastic, metal, glass, paper, wood, or previously coated surfaces.
Solventborne systems usually have lower initial surface tension, but craters can still occur because of contamination, incompatible raw materials, or local surface-tension gradients.
Radiation-curing coatings and inks present another challenge. Their rapid application and curing processes may leave limited time for the additive to migrate to the interface and improve wetting. The selected product must act quickly enough for the coating method and line speed.
A formulation should therefore be evaluated under actual application conditions rather than only through a slow laboratory drawdown.
The best addition stage depends on the additive and formulation.
A substrate wetting additive is often introduced during the let-down or final adjustment stage, allowing its effect to be evaluated after the binder, solvent, pigments, and major additives have been incorporated. However, the technical data sheet and supplier recommendation should determine the initial procedure.
When running trials:
Prepare a control formulation without additional wetting additive.
Add the product at the recommended starting level.
Mix under consistent conditions.
Apply the coating to the target substrate.
Compare wetting, craters, flow, gloss, adhesion, and foam.
Increase the dosage gradually only when necessary.
Adding a large amount immediately can hide the true source of the defect and may introduce new problems.
Surface additives rarely affect only one property. A product selected for wetting may also influence foam, slip, intercoat adhesion, gloss, recoatability, or surface feel.
Excessive surface activity can sometimes stabilize foam or create compatibility problems. A strong or poorly incorporated defoamer can also become a source of cratering in waterborne systems.
For this reason, the wetting additive and defoamer should be evaluated together. A formulation that looks satisfactory during mixing may behave differently during spray application, roller coating, curtain coating, or high-speed printing.
Formulators should monitor:
Foam generation during mixing
Air release after application
Craters and pinholes
Surface slip
Adhesion between coats
Printability or overcoating
Gloss and distinctness of image
The goal is not to achieve the lowest possible surface tension, but to reach sufficient wetting without damaging other film properties.
Static surface-tension data can help compare formulations, but many industrial processes create new surfaces very quickly. High-speed printing, spraying, rolling, and curtain coating may require rapid additive movement at the liquid-air and liquid-substrate interfaces.
Dynamic wetting should therefore be assessed using:
The actual substrate
Normal line speed
Production film thickness
Standard drying or curing conditions
Typical temperature and humidity
Existing pretreatment and cleaning methods
Contact-angle measurements, drawdowns, spray panels, print tests, and visual defect counts can all support the evaluation. The most useful test is the one that closely reproduces production conditions.
One common mistake is trying to correct a contaminated substrate only by increasing wetting-agent dosage. The additive may improve spreading, but it cannot replace proper cleaning and pretreatment.
Other mistakes include:
Testing only on a high-energy laboratory panel
Ignoring changes in substrate suppliers
Adding several surface additives at the same time
Using excessive dosage
Evaluating wetting without checking adhesion
Ignoring the interaction with defoamers
Changing mixing conditions between trials
Approving a formulation without production-line testing
A controlled formulation matrix is more reliable than repeated unrecorded adjustments.
Improving substrate wetting requires coordinated control of substrate cleanliness, surface energy, coating surface tension, additive compatibility, application speed, and curing conditions.
A wetting additive such as TEGO Wet 270 can support crater prevention, flow, and coverage across waterborne, solventborne, and radiation-curing systems, but the final dosage must be confirmed in the actual formulation and application process. By troubleshooting the complete system instead of treating every defect as an additive shortage, formulators can achieve more stable application and a more uniform finished surface.
Vice Chairman of the Coatings and Adhesives Association
Senior New Materials R&D Engineer
Bachelor of Engineering
General Manager
Professional Experience: With 10 years of experience in the fine chemical industry, the team has served over 10,000 clients. Committed to providing one-stop fine chemical services for global clients and helping them optimize the selection of chemical materials.
