{"id":10875,"date":"2026-07-26T00:00:13","date_gmt":"2026-07-26T00:00:13","guid":{"rendered":"https:\/\/longchangchemical.com\/?p=10875"},"modified":"2026-08-09T12:30:14","modified_gmt":"2026-08-09T12:30:14","slug":"2k-pu-basecoat-additives","status":"publish","type":"post","link":"https:\/\/longchangchemical.com\/de\/2k-pu-basecoat-additives\/","title":{"rendered":"2K PU Basecoat Additives: Wetting vs Reactive Routes"},"content":{"rendered":"

2K PU basecoat additives<\/strong> should be chosen only after the formulator separates three questions: does the wet film enter the substrate, does the surface flow without craters, and will a hydroxyl-functional additive change the NCO\/OH calculation? Those are different problems. Treating every silicone as a late-stage leveling aid can improve appearance on one panel while changing pot life, cure, intercoat adhesion, or the next coat.<\/p>\n

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1. Wetting failure<\/strong>
Screen CHLUMIWE\u00ae 3071 at controlled dose.<\/div>\n
2. Reactive surface route<\/strong>
Recalculate NCO\/OH before CHLUMIAG\u00ae 3467.<\/div>\n
3. Film approval<\/strong>
Check cure, recoat, adhesion and abrasion.<\/div><\/div>
Original 2K PU basecoat map: diagnose wetting first, then gate reactive additives by stoichiometry.<\/figcaption><\/figure>\n

Define the basecoat failure before choosing an additive<\/h2>\n

A 2K polyurethane basecoat is normally an appearance-setting and intercoat-critical layer. Record the resin and hardener, NCO\/OH target, pigment package, substrate or preceding primer, film build, induction time, pot-life interval, flash, cure and planned topcoat. Then classify the defect. Retraction at the panel edge, craters around contamination, orange peel, entrained air and poor intercoat adhesion require different experiments.<\/p>\n

Make equal-thickness panels with one unchanged control. ASTM D823<\/a> describes practices for producing uniform coating films on test panels. Uniform application does not reproduce every production spray condition, but it prevents film-build variation from being mistaken for an additive benefit.<\/p>\n

Evidence-based first routes<\/h2>\n\n\n\n\n\n\n\n
Route<\/th>\nPublic product-page evidence<\/th>\nStarting decision<\/th>\nImportant boundary<\/th>\n<\/tr>\n<\/thead>\n
CHLUMIWE\u00ae 3071<\/a><\/td>\nPolyether-modified polysiloxane; low surface tension; wetting, spreading and penetration; 0.1\u20131.0% of total formulation<\/td>\nUse when substrate entry or flow is the first measurable failure<\/td>\nThe public page gives no active-content value and warns that it may stabilize foam in waterborne systems<\/td>\n<\/tr>\n
CHLUMIAG\u00ae 3467<\/a><\/td>\nHydroxyl-functional reactive leveling route; anti-cratering, wetting and leveling; public hydroxy value is only stated as \u226485 mg KOH\/g<\/td>\nConsider when a bound-in surface effect is required and the formulation owner can recalculate stoichiometry<\/td>\nThree dose bases are published; the hydroxy-value limit is not an exact batch value<\/td>\n<\/tr>\n
CHLUMIFE\u00ae 3370<\/a><\/td>\nReactive hydroxyl polyester-modified polysiloxane for 2K PU; 0.05\u20133% of total formulation; solvent\/UV, not waterborne<\/td>\nEvidence-gated candidate for smoothness and gloss in a compatible solvent-based 2K PU package<\/td>\nNo public hydroxyl value is supplied; it is a waxy solid with an initial melting point \u226550\u00b0C<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Use 3071 for a non-stoichiometric wetting screen<\/h2>\n

3071 is the clearer first benchmark when the basecoat has poor spread on metal, plastic or another difficult surface. The product page supports wetting, penetration, flow, leveling, recoatability and gloss retention across waterborne, UV, solvent and high-solids systems. That is useful evidence, but it does not prove performance in a particular pigmented 2K PU basecoat.<\/p>\n

Run a low\/mid\/high ladder inside the published 0.1\u20131.0% range, with the control held at identical viscosity and film build. Do not call the top dose \u201cbest\u201d because it gives the lowest surface tension. Excess surface activity can alter foam, slip, crater sensitivity, recoat or adhesion. In a waterborne 2K PU route, include a foam observation because the current product page explicitly warns of foam stabilization.<\/p>\n

3467 changes the reaction calculation<\/h2>\n

3467 is not a drop-in equivalent to 3071. Its hydroxyl groups may react with isocyanate. The public page gives a hydroxy value of no more than<\/em> 85 mg KOH\/g, not a certificate value for the delivered batch. Therefore, an exact NCO demand cannot be calculated from the website alone. Obtain the current TDS and COA, confirm the analytical basis, and include the additive OH contribution in the formulation\u2019s equivalent-weight calculation.<\/p>\n

The published dosage also uses three different denominators: 0.05\u20131% of total formulation for solvent systems, 0.5\u20135% of resin for resin modification, and 0.5\u20135% of total formulation for waterborne systems. Never place those numbers in one equal-dose ladder. Record whether 3467 is introduced during polyol prepolymerization or by direct coating modification, because the incorporation route can change the reaction opportunity and test result.<\/p>\n

Keep 3370 behind an evidence gate<\/h2>\n

3370\u2019s public description supports reaction with isocyanate and use in two-component polyurethane crosslinking systems. However, the page does not publish a hydroxyl value. It also identifies a 100%-solid waxy material, an initial melting point of at least 50\u00b0C, alkane\/aromatic dilution, and no waterborne suitability. Those facts make temperature, dissolution and equivalent-weight data essential.<\/p>\n

Do not add 3370 to a live formula based only on the broad 0.05\u20133% dosage range. Request the current OH value, recommended melting or incorporation procedure, compatibility evidence and batch certificate. Until those are available, 3370 is a supplier-assisted candidate, not a first blind screening route.<\/p>\n

Build a small test matrix<\/h2>\n\n\n\n\n\n\n\n\n\n
Variable<\/th>\nControl<\/th>\nScreen<\/th>\nRecord<\/th>\n<\/tr>\n<\/thead>\n
Zusatzstoff<\/td>\nNo surface additive change<\/td>\nOne product family at a time<\/td>\nAs-supplied dose and confirmed active basis<\/td>\n<\/tr>\n
2K reaction<\/td>\nOriginal NCO\/OH<\/td>\nRecalculated NCO\/OH for reactive candidates<\/td>\nCOA OH value, mix time, induction and pot-life age<\/td>\n<\/tr>\n
Anmeldung<\/td>\nFixed viscosity and film build<\/td>\nSame gun\/drawdown settings<\/td>\nTemperature, humidity, flash and cure<\/td>\n<\/tr>\n
Surface<\/td>\nReference panel<\/td>\nWetting, crater count, orange peel and gloss<\/td>\nDefined observation time and instrument settings<\/td>\n<\/tr>\n
Downstream<\/td>\nReference recoat<\/td>\nRecoat, tape adhesion and abrasion<\/td>\nFailure locus and aged result<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Test cure and pot life, not only fresh appearance<\/h2>\n

A reactive additive can look excellent immediately and still shift cure behavior. Compare viscosity and sprayability at the start, midpoint and end of the claimed pot-life window. Measure tack-free or handling time using the plant\u2019s agreed method, then repeat gloss, hardness or solvent resistance after full cure. If the formulation has an induction period, keep it identical across all panels.<\/p>\n

For reactive routes, approve only after an exact NCO\/OH calculation based on current supplier data. The public upper limit for 3467 is a screening warning, not a substitute for the batch value. For 3370, the missing public OH value prevents a defensible calculation entirely.<\/p>\n

Protect recoat and adhesion<\/h2>\n

The basecoat is not finished when it looks smooth. Apply the intended next coat at the minimum and maximum recoat windows. Use ASTM D3359<\/a> as an agreed tape-adhesion reference for coated metal, while recording whether failure occurs at metal\/basecoat, within the basecoat, or between basecoat and topcoat. The method is an indicator and is not sensitive to small differences at high adhesion levels, so keep a practical recoat or pull-off test where the specification requires it.<\/p>\n

Check abrasion without over-reading one number<\/h2>\n

If the basecoat is exposed during handling or must survive assembly before topcoating, screen abrasion after the specified cure. ASTM D4060<\/a> can compare organic coatings on rigid panels, but wheel type, load, cycles, film thickness and debris handling must be fixed. A lower mass loss does not automatically prove better intercoat behavior or field durability.<\/p>\n

Decision rules for the first sample request<\/h2>\n