Waterborne appliance sealer additives should be chosen around the sealer’s real job: uniform coverage, correct cure and reliable bonding to the next coat. Surface smoothness alone is not release evidence. Fix cleaning, pretreatment, resin chemistry, film build and bake first; then screen wetting and flow routes one variable at a time.
Substrate, cleaning and pretreatment.
Coverage, film build and bake.
Basecoat adhesion and appearance.
Define the sealer and stack
Record whether the layer seals metal, a porous filled surface or another coating; whether it is pigmented or clear; and what primer, basecoat or topcoat follows. Document substrate, cleaning, pretreatment, resin, crosslinker, pigments, solids, pH, viscosity, wet and dry film, flash, oven profile and peak part temperature. A formulation cannot be judged without its complete stack.
Prove cure before surface adjustment
Under-cure can look like poor leveling, tack, weak abrasion or intercoat failure. Over-bake can embrittle the film or reduce recoat acceptance. Use an agreed cure indicator, record time at metal temperature and condition panels before testing. Hold film thickness and bake constant when additives are compared.
Separate the three routes
| Route | Published facts | First justified use | Critical boundary |
|---|---|---|---|
| 3071 | 0.1–1.0%; water/solvent/UV; surface tension <25 mN/m | Verified wetting or spreading deficit | May stabilize foam in waterborne systems |
| 3345 | 100% active; 0.1–1.0%; water/solvent/UV | Measured flow/leveling defect | Compatibility and recoat still require proof |
| 3467 | 100% active; waterborne 0.5–5%; OH ≤85 mg KOH/g | Compatibility/leveling study after chemistry review | Upper-limit OH cannot support exact stoichiometry |
Screen 3071 for difficult wetting
Use 3071 when clean, correctly prepared panels still show edge pullback, skips or poor spreading. Its page allows grind, stirring or post-production addition and recommends 0.1–1.0% of total formulation. Start low, hold application settings constant and measure defect count instead of relying only on a visual impression.
The same page warns that 3071 may stabilize foam in water-based systems. Track wet density, foam persistence, microbubbles and pinholes through mixing, pumping and spray or roll application. If wetting improves while air defects rise, do not hide the tradeoff with an uncontrolled second additive.
Screen 3345 for film flow
3345 is a 100% active polyether-modified polysiloxane with a published 0.1–1.0% range. It may be added during grinding, stirring or after production; the page also notes that dipropylene glycol methyl ether can enhance its effect. Any co-solvent change must be included in VOC, flash, cure and compatibility review.
Use it only after rheology, atomization or roll settings, flash and bake are controlled. Measure orange peel or waviness, gloss, crater count and film build. Then test sealer-to-basecoat adhesion; improved flow does not prove that the next layer will bond.
Gate 3467 by reaction evidence
3467 can be screened within its published waterborne range as a compatibility/leveling route. Its OH ≤85 mg KOH/g value is not an exact batch value. For a two-component polyurethane, a reaction calculation needs batch OH, resin OH, isocyanate equivalent weight, solids and the target NCO/OH ratio. For a bake system, obtain the relevant cure evidence and schedule.
Without those inputs, do not present 3467 as permanently incorporated into the network. Treat it as a controlled surface-modifier trial and verify cure, intercoat adhesion, solvent resistance, gloss and service properties.
Use a staged matrix
| Stage | Panel set | Measure | Stop condition |
|---|---|---|---|
| Baseline | Current formula, controlled process | Cure, wetting, flow, air | Process defect remains unexplained |
| Wetting | 3071 low/mid/high | Coverage and crater count | Persistent foam or pinholes |
| Flow | 3345 low/mid/high | Appearance and gloss | Recoat adhesion declines |
| Chemistry | 3467 after document review | Compatibility and cure | Stoichiometry or bake evidence absent |
Measure adhesion on the complete stack
ASTM D3359 covers tape-test assessment of relatively ductile coatings on metal. Specify film thickness, method, tape, conditioning and failure plane. In a multicoat appliance stack, identify whether failure is substrate/sealer, within the sealer or sealer/basecoat; a single rating without the plane can conceal the real problem.
Measure appearance and wear honestly
ASTM D523 measures specular gloss; keep geometry, calibration, panel curvature and film thickness consistent. If abrasion matters, ASTM D4060 provides a comparative Taber abrasion method. Wheel, load, cycles, conditioning and endpoint must be agreed. Neither test alone proves cleaning-chemical, humidity, heat or final appliance durability.
Advance to representative service tests
Apply the full coating stack and condition it for the agreed time. Check recoating window, adhesion, gloss, color, hardness, abrasion, humidity, detergent or chemical exposure, heat and edge performance as the product specification requires. Include vertical and horizontal orientations if sag and leveling differ on the appliance geometry.
Decision rules
- Reject a smoother sealer if cure or recoat adhesion falls.
- Use 3071 for verified wetting while monitoring foam stabilization.
- Use 3345 for verified flow within its published range.
- Use 3467 reactively only with exact chemistry and cure evidence.
Information to send
Provide substrate and pretreatment, full layer stack, resin/crosslinker, solids, pH, rheology, application, film build, flash and bake, first defect, recoat window and required appearance, adhesion, abrasion and service limits.
Ask Longchang for an appliance-sealer trial plan built around your coating stack.