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When craters or fisheyes appear in a coating film, many people first think of poor leveling. But leveling and substrate wetting are not the same thing. Even a coating with good flow can leave local defects if contact with the substrate is incomplete at the start of application, so substrate wetting, film flow and recoat condition should be examined together when adjusting a formulation.
Craters and fisheyes after application are common surface problems in formulation development. The usual reaction is to add more leveling agent in the hope that better film flow will correct the surface. Sometimes, though, craters remain even after leveling has improved. The tables below follow the sequence from the symptom to its cause and to what can be checked.
Problem
Likely cause
What to check
ProblemCraters or fisheyes remain although leveling has improved
CauseLeveling and substrate wetting are two different stages. When the coating first meets the substrate it must form a continuous spread; if wetting is locally insufficient at this point, later flow cannot necessarily correct the surface difference already formed.
What to checkGo back to the initial stage of contact between coating and substrate, instead of only judging flatness after drying.
ProblemThe same formulation fails on a different substrate
CauseMetal, plastic and workpieces with different surface treatments differ in surface energy, cleanliness and surface state, so the same coating may spread normally on one and show local shrinkage, insufficient wetting or fisheyes on another.
What to checkRe-check the balance between wetting and leveling; simply raising an ordinary leveling agent may not solve it.
ProblemSubstrate surface
CauseOil, release agent or other factors that affect wetting.
What to checkConfirm whether the substrate surface carries oil stains, release agent or similar contamination.
ProblemApplication state
CauseSpray thickness, application speed and environmental conditions can change how the wet film forms.
What to checkCheck these application factors.
ProblemAdditive adjustment
CauseWith resin, pigment and solvent basically unchanged, different DH-3077 ratios can show whether the problem lies more in substrate wetting or in the film's own flow.
What to checkCompare defect count, defect area and film flatness at each ratio.
DH-3077: adjusting from the substrate-wetting side
DH-3077 is a fluorine-modified acrylate copolymer leveling agent with a content of 70% and xylene as solvent. Compared with the conventional leveling approach, the fluorine-modified structure can work by lowering the surface tension of the system and improving interfacial spreading. Three aspects deserve attention in a formulation:
- Substrate wetting. On substrates where the coating spreads poorly, observe the contact between wet film and substrate after adding DH-3077.
- Film leveling. While wetting improves, also observe the flatness and uniformity of the dried film.
- Recoat performance. If the product needs several coats, do not judge only the first coat; run a recoat test to see how the next layer spreads and bonds.
How to think about the dosage
The reference dosage of DH-3077 is 0.2%-1% of the total formulation. It is not advisable to add a single fixed ratio and judge the result; set several gradients according to resin type, substrate properties and application method. The points to observe are:
- spreading state of the wet film on the substrate;
- craters, fisheyes and other surface defects;
- flatness of the dry film;
- gloss and appearance of the film;
- surface state after recoating;
- adhesion between film and substrate.
If a low dosage already meets the requirement of the current system, the ratio can be confirmed further together with other performance.
Frequently Asked Questions
Why do craters remain when leveling is already good?
Substrate wetting and film leveling are two different stages. If wetting is locally insufficient when the coating first meets the substrate, later flow cannot necessarily correct the surface difference that has formed.
Why can the same formulation fail on a different substrate?
Metal, plastic and workpieces with different surface treatments differ in surface energy, cleanliness and surface state, which can cause local shrinkage, insufficient wetting or fisheyes.
What is DH-3077?
A fluorine-modified acrylate copolymer leveling agent with a content of 70% and xylene as solvent, which can work by lowering surface tension and improving interfacial spreading.
What is the reference dosage of DH-3077?
0.2%-1% of the total formulation, tested in several gradients according to resin type, substrate properties and application method.
Summary. When craters and fisheyes appear, leveling is only one direction to look at. From contact with the substrate to a formed film, the coating goes through wetting, spreading, flow and drying, and a difference in any stage may show up on the final surface. When adjusting the leveling agent, look at substrate wetting and film leveling together, and add a recoat test. DH-3077, a fluorine-modified acrylate copolymer leveling agent with a reference dosage of 0.2%-1%, can be tested in gradients according to the resin system, substrate and application conditions to fix the ratio.
