Risposta rapida: the best additive for UV primer cratering depends on why the crater is forming. If the first problem is poor wetting and spreading, a wetting route such as CHLUMICRYL® WD-D547 deserves earlier review. If the system is a solvent-based UV primer with persistent crater pressure, anti-shrinkage stress, or a silicone-restricted formulation window, CLUMICRYL® FS-D9013R usually moves up first. If the buyer still needs strong crater control but the process is closer to large-area spraying or varnish-compatible UV work, CLUMICRYL® FS-D8950BR becomes a stronger first route. If the panel is showing more orange peel and spray-flow instability than hard crater pressure, CLUMICRYL® FS-D8980 is often the cleaner comparison point.
This page is narrower than the broader UV coating flow and leveling guide and the wider fluorine surfactant page. It is built for buyers who already know the pain point sits in UV primer anti-cratering and now need a faster first-screen logic.
Why UV primer cratering needs its own selection logic
UV primer work is rarely judged by surface appearance alone. The primer still has to wet the substrate, stay stable during application, control crater formation, and often remain friendly to recoating or downstream topcoat work. That means a crater in UV primer is not always just a generic surface-defect problem.
In practice, buyers usually need to separate four different first questions:
- Is the real issue wetting and spread?
- Is the crater pressure strong enough to require a fluorocarbon rescue route?
- Is the production method closer to spray-applied UV work where large-area application behavior matters?
- Will the primer still need clean recoating afterward?
That split is commercially useful because Longchang’s current CHLUMICRYL® pages already support different answers for those different first problems.
When to start with wetting, and when to move to a crater-control route
| Observed UV primer problem | Best first route | Why |
|---|---|---|
| Poor spread, weak coverage, or unstable wetting before the crater pattern fully develops | WD-D547 | The first failure is still how the primer reaches and covers the surface |
| Persistent cratering or anti-shrinkage pressure in solvent-based UV primer, especially with silicone restrictions | FS-D9013R | Longchang directly supports it for strong anti-cratering and silicone-restricted UV primer logic |
| Crater control plus varnish compatibility and large-area spraying matter together | FS-D8950BR | The supported fit is solvent-based UV cure with anti-cratering, varnish compatibility, and large-area spray relevance |
| Orange peel and spray-flow uniformity matter more than the strongest crater-rescue route | FS-D8980 | The supported positioning is good long-wave leveling and orange-peel prevention in solvent-based UV cure |
| Visible air or foam behavior is the real root cause | Defoamer route | Do not ask a surface-control additive to solve a true air-management problem |
CHLUMICRYL® routes to review first for UV primer anti-cratering
1. WD-D547 when the crater starts as a wetting and spreading failure
CHLUMICRYL® WD-D547 is supported by Longchang for water-borne paint, solvent and solvent-free paint, and UV cure paint. The product page states that it most effectively reduces the surface tension in water systems and provides excellent wetting and spreading together with anti-cratering, re-coating, defoaming, and leveling. The suggested addition range is Da 0,1% a 0,5%.
That makes WD-D547 a practical first route when the UV primer is not yet laying down correctly enough for a narrower fluorocarbon route to be the first move. It deserves earlier review when:
- the primer still shows coverage and spread instability,
- the crater pattern looks tied to wetting failure rather than only to stronger surface-tension mismatch,
- the project still needs a route that keeps recoating visible, and
- the team wants a broader first correction before moving to a more specialized fluorine lane.
2. FS-D9013R when solvent-based UV primer needs a stronger anti-cratering answer
CLUMICRYL® FS-D9013R is one of the clearest supported routes for this page. Longchang positions it for solvent-based UV cure and supports it with good long-wave leveling, orange-peel prevention, excellent anti-cratering ability, fast leveling speede high-temperature resistance. The product page also says it could recoating and is often used as an anti-shrinkage additive in systems where silicone additives cannot be used. Longchang further notes that it gives an excellent anti-cratering effect in common UV primer without affecting recoating, while also warning that it is not applicable in UV vacuum electroplating primer because it will affect recoating. The suggested addition range is 0.1% to 1.0%.
That makes FS-D9013R the stronger first route when:
- the formulation is clearly a solvent-based UV primer,
- the crater problem remains after more ordinary wetting or leveling changes,
- silicone restriction matters in the project window, or
- the team needs a supported route for common UV primer work that still respects recoating, but not UV vacuum electroplating primer.
3. FS-D8950BR when anti-cratering, varnish compatibility, and spray application matter together
CLUMICRYL® FS-D8950BR is also supported for solvent-based UV cure, but with a slightly different commercial logic. Longchang supports it with good compatibility in varnish, good long-wave leveling, orange-peel preventione excellent anti-cratering ability. The same page also states that it is suitable for large-area spraying, has no foam inhibition, and can help prevent color channeling between colors after wet spraying and drying. The suggested addition range is 0.1% to 1.0%.
That pushes FS-D8950BR forward when:
- the UV primer or related UV underlayer is being applied in a spray-oriented process,
- the buyer still needs strong crater control,
- varnish compatibility matters in the surrounding formulation logic, and
- the team wants a supported fluorocarbon route that fits large-area spraying more directly.
The watchpoint is useful too. Longchang explicitly says the product has no foam inhibition, so it should not be used as a substitute for a true defoamer when the real defect starts with trapped air.
4. FS-D8980 when the bigger issue is orange peel and spray-flow behavior
CLUMICRYL® FS-D8980 is another solvent-based UV cure fluorocarbon route, but its supported role is a little cleaner when the problem is more about leveling and orange-peel prevention than about the strongest crater rescue. Longchang supports it with good compatibility in varnish, good long-wave leveling, orange-peel prevention, suitability for large-area spraying, and prevention of color channeling between colors after wet spraying and drying. The suggested addition range is 0.05% to 0.8%.
FS-D8980 belongs earlier when:
- the UV primer panel is showing spray-flow inconsistency e orange peel,
- the crater pressure is present but not clearly as dominant as in a 9013R-led route,
- the buyer still wants a varnish-compatible fluorocarbon path, and
- the team wants a lower-dose comparison route before escalating.
How buyers should narrow the first sample round
Start with the defect stage
If the primer is still failing at the wetting and spreading stage, begin with WD-D547. If the film already wets but still forms stubborn craters, move into the fluorocarbon route sooner.
Keep recoating visible from the beginning
UV primer work is not only about the first panel looking better. The primer still has to fit the next layer. That is why Longchang’s recoating note on FS-D9013R matters so much.
Separate crater rescue from spray optimization
FS-D9013R is stronger when the discussion is about hard crater pressure and silicone-restricted primer logic. FS-D8950BR and FS-D8980 become more attractive when the process is closer to spray application, varnish compatibilitye orange-peel management.
Do not confuse air-management defects with surface-control defects
Once Longchang tells you that FS-D8950BR and FS-D8980 have no foam inhibition, that is a useful warning. If the defect is really coming from foam or trapped air, move that sample round back toward a defoamer path instead of asking the fluorocarbon route to solve the wrong problem.
Keep the first screen short
For most buyers, the cleanest first screen is one wetting-led route, one crater-heavy fluorocarbon route, and one spray-flow fluorocarbon route. That usually teaches more than testing too many overlapping additives at once.
Recommended Longchang path from this page
- Overview page: CHLUMICRYL® Additivi per vernici e inchiostri
- Related function page: How to Choose Wetting Additives for Coatings and Inks
- Related function page: How to Choose Fluorine Surfactants for Surface Control in Coatings and Inks
- Related application page: How to Improve Flow and Leveling in UV Coatings
- Related application page: Surface Control Additives for UV Varnishes and Overprint Systems
- Related comparison page: FS-D9013R vs FS-D8950BR vs FS-D8980
FAQ
What is the best first additive when a UV primer still does not spread correctly?
Start with WD-D547 earlier because Longchang directly supports it with wetting, spreading, anti-cratering, recoating, defoaming, and leveling across water-borne, solvent, solvent-free, and UV cure paint systems.
When should FS-D9013R move ahead of FS-D8950BR?
FS-D9013R should move ahead when the project is a solvent-based UV primer with stronger crater pressure, anti-shrinkage needs, or silicone restrictions, especially when common UV primer recoating still matters.
Why would a buyer start with FS-D8950BR instead of FS-D8980?
Start with FS-D8950BR when anti-cratering remains a stronger priority and the process also depends on varnish compatibility or large-area spraying. FS-D8980 is the cleaner first route when leveling and orange-peel control are more dominant than hard crater rescue.
Can FS-D9013R be used in every UV primer?
No. Longchang explicitly warns that FS-D9013R is not applicable in UV vacuum electroplating primer because it will affect recoating, even though it is supported for common UV primer anti-cratering work.
Need a faster first shortlist for UV primer cratering?
If your UV primer line is losing time to crater defects, stop treating every crater as the same problem. First decide whether the failure is wetting-led, crater-heavy and silicone-restricted, or spray-flow and orange-peel led. That usually leads to the right CHLUMICRYL® route much faster than testing all surface-control additives as if they solved the same first job.