Select 2K PU clearcoat additives by the primary surface requirement and protect the cure balance. CHLUMIAG® 3467 is the compatibility-focused silicone route, CHLUMIFE® 3370 is a waxy-solid feel route for non-waterborne systems, and CHLUMIFE® 3307X is a leveling/scratch-resistance route that prioritizes recoatability. None should be described as a universal cure improver.
Before screening an additive, stabilize polyol and isocyanate batches, NCO/OH calculation, moisture control, induction time, mixed viscosity, pot life, application weight, flash, and cure. A smoother fresh panel can still fail hardness, chemical resistance, intercoat adhesion, or repair after full crosslinking.
2K PU clearcoat additive decision map
| Primary requirement | First route | Non-negotiable guardrail |
|---|---|---|
| Broad compatibility and surface control are the first concern | CHLUMIAG® 3467 | Pot life, cure, hardness, adhesion, and final feel |
| A waxy/silky tactile profile is required in a solventborne clearcoat | CHLUMIFE® 3370 | Dispersion, clarity, gloss, recoating, and warm aging |
| Leveling/scratch performance is needed while repair or recoating matters | CHLUMIFE® 3307X | Follow dilution guidance; verify intercoat adhesion and solvent compatibility |
| Produk | Published facts | Supplier starting guidance | Important boundary |
|---|---|---|---|
| CHLUMIAG® 3467 | Multi-component modified polysiloxane; 100% active; hydroxyl value ≤85 mg KOH/g | 0.05–1% in solvent systems; separate resin-modification guidance also published | Prioritizes compatibility; supplier notes that feel is less refined |
| CHLUMIFE® 3370 | Multi-component modified polysiloxane; waxy solid; initial melting point ≥50°C | 0.05–3%; UV and solvent systems | Not published as water-based or as a reactive 2K PU additive |
| CHLUMIFE® 3307X | Polyether-modified polysiloxane; 100% active; UV and solvent systems | Dilute to 12.5% as directed; use 0.1–1% of total formulation | Supplier positions it toward recoatability rather than maximum smoothness |
Use 3467 when compatibility is the first risk
3467 is the logical starting comparison when the formulation needs broad surface control but incompatibility, haze, or cratering risk limits aggressive silicone choices. Its product page lists solvent, UV, and water-based use and says compatibility is prioritized over a more refined feel.
The supplier also publishes a separate polyurethane resin-modification route, including addition with the polyol during prepolymerization. Do not transfer that instruction automatically to a finished commercial 2K pack. Resin modification and post-addition coating adjustment are different experiments; confirm the intended route, recalculate reactive balance where applicable, and obtain current technical guidance.
Use 3370 for waxy feel, not as a claimed reactive route
3370 is a waxy solid with a published initial melting point of at least 50°C and a 0.05–3% range for UV and solvent systems. Its useful screening purpose in a 2K PU clearcoat is tactile modification. The public product facts do not support calling it a reactive additive.
Document incorporation temperature, mixing energy, order of addition, and cooling history. Inspect clarity and haze at the actual dry-film thickness, then repeat feel, gloss, abrasion, repair adhesion, and warm-storage checks. Surface migration or incomplete dispersion may not be visible on a fresh panel.
Use 3307X when recoating is a required guardrail
3307X is a polyether-modified polysiloxane positioned for leveling and scratch resistance while prioritizing recoatability. The supplier instructs dilution to 12.5% with a xylene/ethylene glycol monophenyl ether blend at 7/2 before use, followed by a 0.1–1% dosage based on total formulation.
Confirm that this solvent route is compatible with the factory’s handling, regulatory, and formulation requirements. Compare initial leveling and scratch response together with intercoat adhesion, repair-window behavior, cratering, gloss, haze, and pot life. “Prioritizes recoatability” is a reason to test, not a guarantee in every resin and cure package.
Protect NCO/OH balance and pot life
- Calculate the control formulation. Record polyol hydroxyl value, isocyanate NCO content, solids, moisture, catalyst, and target index.
- Choose the addition route. Distinguish a nonreactive coating-stage comparison from any supplier-supported resin modification.
- Measure mixed behavior. Track induction time, viscosity rise, usable pot life, appearance, and sprayability at fixed intervals.
- Hold application constant. Use the same substrate, primer, film weight, flash, temperature, humidity, and cure.
- Condition fully. Evaluate both early handling and final properties at the agreed cure age.
Use a controlled clearcoat validation matrix
Compare a blank with a small dosage ladder for one product at a time. Record leveling, orange peel, craters, gloss, haze, clarity, color, sag, dry-to-touch, pot life, hardness development, solvent and chemical resistance, abrasion, scratch/mar, adhesion, and recoat/repair performance. Repeat the preferred condition after warm aging and on production equipment.
ASTM D523 describes specular-gloss measurement, ASTM D3363 covers pencil film hardness, ASTM D4060 covers Taber abrasion for suitable planar rigid specimens, and ASTM D3359 covers tape adhesion ratings. Select the methods that match the substrate and define conditioning, film thickness, repair interval, and pass/fail limits before testing.
Troubleshoot misleading early results
The fresh film looks better, but hardness develops slowly
Recheck mix ratio, moisture, solvent retention, film thickness, catalyst, and cure temperature. Do not approve the surface result until the cure profile matches the control or the agreed specification.
Feel improves, but haze appears after warm storage
Review 3370 incorporation and dosage, then compare at the actual film thickness. Repeat clarity, gloss, and adhesion after the same storage history used for the customer evaluation.
Recoat adhesion varies with repair time
Map several realistic repair windows instead of reporting one result. Clean and prepare panels consistently, and compare 3307X against the blank under the same cure and sanding conditions.
Related additive guides
Use the 2K PU topcoat guide for a broader topcoat diagnosis, the soft-touch coating guide when tactile feel dominates, or the wood varnish guide when the substrate and finishing process are the main constraints.
Frequently asked questions
Is CHLUMIFE 3370 reactive with isocyanate?
The public product page does not document 3370 as a reactive 2K PU additive. Treat it as a waxy-solid surface/feel candidate and do not change NCO/OH assumptions without current supplier evidence.
Does 3307X guarantee recoatability?
No. The supplier says it prioritizes recoatability, but the resin, cure age, surface preparation, and repair coat determine the actual result. Run an application-specific adhesion test.
Can 3467 be added during PU prepolymerization?
The supplier publishes that option for polyurethane modification, but it is a separate formulation route. Confirm technical guidance and account for its hydroxyl value and the full reactive balance before using it.
Request a 2K PU clearcoat comparison
Send the polyol and isocyanate data, NCO/OH target, solids, solvent package, catalyst, moisture controls, substrate, application method, film weight, pot life, cure, defect photos, and repair requirements. Ask Longchang Chemical for a 3467, 3370, or 3307X screening plan.