{"id":10961,"date":"2026-07-31T00:00:07","date_gmt":"2026-07-31T00:00:07","guid":{"rendered":"https:\/\/longchangchemical.com\/?p=10961"},"modified":"2026-08-09T14:37:39","modified_gmt":"2026-08-09T14:37:39","slug":"waterborne-direct-to-metal-clearcoat-additives","status":"publish","type":"post","link":"https:\/\/longchangchemical.com\/nl\/waterborne-direct-to-metal-clearcoat-additives\/","title":{"rendered":"Waterborne DTM Clearcoat Additives: Clarity & Air"},"content":{"rendered":"

Waterborne direct-to-metal clearcoat additives<\/strong> must preserve transparency, metal adhesion and corrosion performance. They cannot replace cleaning, conversion treatment, flash-rust control or cure. Separate process air from polyurethane chemistry, and do not begin with a grade whose own page warns about pinholes and whitening.<\/p>\n

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Clear film carries air<\/strong>
Screen D9904BR in the grind.<\/div>\n
True PU modification<\/strong>
Gate 3467 by exact OH\/NCO.<\/div>\n
Clarity is critical<\/strong>
Exclude 3166 from the first shortlist.<\/div>\n<\/div>
Original waterborne DTM clearcoat map: protect clarity, adhesion and corrosion before surface refinement.<\/figcaption><\/figure>\n

Define the clearcoat function<\/h2>\n

State whether the film is a bare-metal protective clear, decorative transparent layer or clear top layer in a multicoat system. Identify alloy, surface finish, preparation, conversion coating and edge geometry. A transparent film exposes craters, microbubbles, haze, whitening and corrosion more readily than a pigmented layer.<\/p>\n

Control metal preparation<\/h2>\n

Record oil removal, rinse quality, soluble salts, profile, treatment chemistry, treatment age and time to coating. Retain prepared and intentionally unprepared controls from the same metal lot. Additives cannot compensate for contamination, flash rust or unstable conversion treatment.<\/p>\n

Compare the honest first routes<\/h2>\n\n\n\n\n\n\n\n
Route<\/th>\nPublished facts<\/th>\nFirst use<\/th>\nBoundary<\/th>\n<\/tr>\n<\/thead>\n
D9904BR<\/a><\/td>\n30% active in DPM; water-based; 0.1\u20131.0%<\/td>\nAir from high-shear grind<\/td>\nCo-solvent premix\/high shear; post-addition not recommended<\/td>\n<\/tr>\n
3467<\/a><\/td>\n100% active; OH \u226485 mg KOH\/g; three dose bases<\/td>\nDocumented PU reaction or compatibility study<\/td>\nExact OH, NCO, solids and NCO\/OH required for reaction claims<\/td>\n<\/tr>\n
3166<\/a><\/td>\n0.05\u20131.0%; water\/solvent\/UV; surface benefits listed<\/td>\nOnly a later risk-controlled study<\/td>\nOwn page warns of pinholes, whitening and foam stabilization<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Use D9904BR for grind-stage air<\/h2>\n

Premix with an approved co-solvent and add under high shear during grinding. Measure wet density, foam decay, microbubbles, pinholes and haze. Include the DPM carrier and 30% active content in formulation and VOC calculations. Do not convert it into a late after-addition trial.<\/p>\n

Keep 3467 behind the PU gate<\/h2>\n

If the clearcoat is a true polyurethane route, obtain exact batch OH, resin OH, isocyanate equivalent, solids and target NCO\/OH. The public OH value is only an upper limit. Fix induction, pot life and cure. If no NCO reaction exists, treat 3467 only as a compatibility candidate and do not claim grafting or permanent performance.<\/p>\n

Exclude 3166 from the first shortlist<\/h2>\n

A clarity-critical waterborne film should not begin with a product whose public precautions include pinholes, whitening and foam stabilization. If later evidence justifies a 3166 study, run it only after D9904BR and cure controls are understood, with haze, whitening, foam, adhesion and corrosion as explicit stop conditions.<\/p>\n

Use a controlled matrix<\/h2>\n\n\n\n\n\n\n\n\n
Set<\/th>\nChange<\/th>\nPrimary measure<\/th>\nRelease gate<\/th>\n<\/tr>\n<\/thead>\n
A<\/td>\nPrepared control<\/td>\nClarity, air, cure and adhesion<\/td>\nWater\/corrosion\/recoat<\/td>\n<\/tr>\n
B\u2013D<\/td>\nD9904BR low\/mid\/high<\/td>\nDensity, foam, haze and pinholes<\/td>\nCrater, storage and corrosion<\/td>\n<\/tr>\n
E\u2013G<\/td>\n3467 after chemistry approval<\/td>\nCompatibility\/reaction<\/td>\nPot life, cure and adhesion<\/td>\n<\/tr>\n
H<\/td>\nPreparation correction<\/td>\nRoot-cause comparison<\/td>\nRepeat full system<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Prepare uniform clear films<\/h2>\n

ASTM D823<\/a> describes practices for uniform test films. Fix metal, preparation, application, wet\/dry thickness, flash, temperature, humidity and cure. Measure build near edges as well as flats because thin edges can dominate corrosion.<\/p>\n

Measure gloss and haze separately<\/h2>\n

ASTM D523<\/a> covers specular gloss. Record geometry, substrate appearance and film condition. Add haze, clarity, color shift and visual whitening because gloss alone can rise while transparency worsens.<\/p>\n

Read appearance over a standardized dark and bright metal reference as well as the production finish. Photograph at fixed lighting and viewing angles. Track the same panels after water, humidity and corrosion recovery because temporary whitening or edge haze may appear only after exposure.<\/p>\n

Check adhesion with context<\/h2>\n

ASTM D3359<\/a> provides tape adhesion methods for metallic substrates. Record failure location, film thickness and conditioning. Test after full cure, water\/humidity exposure and any recoat, not only on a fresh dry panel.<\/p>\n

Use replicate panels.<\/p>\n

Validate corrosion as a system property<\/h2>\n

ASTM B117<\/a> describes salt-spray apparatus and operation, but it does not prescribe a universal exposure or predict service life. Define scribe, duration and acceptance. Compare rust, blistering, undercut and adhesion after recovery.<\/p>\n

Check abrasion and cleaning<\/h2>\n

Use the agreed wheel\/load\/cycles or production cleaning protocol at controlled cure age. Record mass or gloss change, breakthrough, haze and metal exposure. Better slip or feel does not prove protection when the clear film thins or loses adhesion.<\/p>\n

Include fingerprints, alkaline cleaner, detergent or other service contaminants only when relevant to the part. Define concentration, dwell, rinse and recovery. Inspect corrosion beneath any damaged area and remeasure adhesion; a cosmetically smooth film is unacceptable if cleaning opens the metal interface.<\/p>\n

Decision rules<\/h2>\n