During construction in high humidity conditions such as high humidity, rainy weather, coastal areas, underground pipe galleries, tunnels, kitchens and bathrooms, fireproof coatings face fatal problems such as moisture absorption, water solubility precipitation, coating foaming and peeling, carbon layer water absorption collapse, sudden drop in flame retardant level, and insulation failure. Ordinary flame retardants, due to their high water solubility, weak interfacial bonding, and poor hydrolysis resistance, quickly fail in long-term humid and hot environments, directly leading to fire safety failure, engineering rework, and safety risks.
1. Water soluble migration and precipitation: Small molecule flame retardants such as ordinary ammonium polyphosphate (APP), pentaerythritol, melamine, etc. have strong polarity and high water solubility. After long-term moisture absorption/immersion, they migrate to the surface of the coating, resulting in an imbalance of flame retardant components and synergistic failure.
2. Collapse of carbon layer due to water absorption: The expanded carbon layer generated by combustion contains hydrophilic groups. When it comes into contact with water, the pores absorb water, the structure softens and disintegrates, losing its ability to insulate heat and oxygen, and the risk of reignition increases dramatically.
3. Interface debonding and coating damage: Flame retardants absorb moisture and form water gaps at the filler resin interface, reducing coating adhesion and mechanical strength, causing foaming, cracking, and peeling, completely losing fire protection.
-High humidity (RH ≥ 85%), condensed water, spray, long-term immersion, salt spray corrosion
-Rapid curing, low moisture absorption, hydrolysis resistance, and long-term stable flame retardant performance after construction
-Compliant with global safety and environmental standards such as UL, GB, IEC, RoHS, REACH, etc
Abandoning traditional halogenated systems (high toxicity, corrosion, limited environmental protection), priority should be given to halogen-free, low smoke, low toxicity, and hydrolysis resistant phosphorus nitrogen boron inorganic hydroxide composite systems.
-Aggregation degree n ≥ 1000, preferably n ≥ 2000 long-chain APP, significantly reduces water solubility and moisture absorption rate.
-Microcapsule encapsulation modification: Silane/epoxy/melamine resin encapsulation forms a hydrophobic barrier, blocking the penetration of water molecules.
-Indicator requirements: Moisture absorption rate ≤ 1.0% at 25℃/90% RH, precipitation rate ≤ 0.5% after 72 hours of static water immersion.
-Using polybutylene glycol, esterified polyol, hyperbranched polyester, and siloxane modified carbon agent, with high molecular weight, low polarity, and insolubility in water.
-Preferred reactive carbon forming agent that can covalently bond with resin to prevent physical migration.
-Using melamine polyphosphate (MPP), melamine cyanurate (MCA), and melamine resin modified foaming agent, low water solubility, high heat resistance, and synchronized foaming.
-Match the decomposition temperature with the acid source/carbon source to ensure continuous and dense expansion of the carbon layer.
1. Magnesium hydroxide (MDH): decomposition temperature of 340-490℃, endothermic dehydration, formation of dense ceramic layer, smoke suppression, non-toxic, and better water resistance than ATH.
2. Zinc borate (ZB): It forms a glassy molten layer at high temperatures, promotes carbonization, suppresses smoke and smoldering, prevents rust and mold, and synergistically improves water resistance with phosphorus based materials.
3. Nano hydrophobic fillers: Nano SiO₂, montmorillonite, talc powder, enhance the density and hydrophobicity of the carbon layer.
-Add silane coupling agent, maleic anhydride graft resin, and fluorosilicone hydrophobic additive to enhance the interfacial adhesion between flame retardant and resin, and reduce water absorption rate.
-The introduction of lotus leaf effect hydrophobic structure on the coating surface reduces water infiltration and penetration.
-Static water immersion precipitation rate: soaking in deionized water at 25 ℃ for 24h/72h/168h, with a mass loss of ≤ 1.0% and extremely low ion precipitation concentration.
-Moisture absorption rate: Excellent for 168 hours of wet heat aging at 85 ℃/85% RH, with a weight gain of ≤ 1.5%.
-Water resistance: No foaming, cracking, or peeling after soaking for 240 hours; There is no softening or peeling after soaking for 720 hours.
-Initial grade: UL94 V-0, GB14907 fire resistance limit meets the standard, LOI≥32。
-After soaking in water: After soaking for 72 hours and drying, the flame retardant level does not degrade, there are no droplets, and there is no rapid reignition.
-Cone calorimeter: After wet heat aging, PHRR and THR increase by ≤ 10%, and the carbon layer remains stable.
-After immersion, the carbon layer does not pulverize, does not absorb water and collapse, remains continuous and intact, and has a contact angle of ≥ 90 ° (hydrophobic).
-Adhesion ≥ 1.5MPa, compressive strength ≥ 2MPa, retention rate after immersion ≥ 80%.
-Good leveling performance, fast curing, no sagging, suitable for construction on damp substrates.
-Selection: Microcapsule coated high polymer APP+MPP+hydrophobic MDH+zinc borate composite system
-Requirements: 720h water resistance, 500h no corrosion from salt spray, flame retardant V-0 retention, and hydrophobic coating that does not peel off.
-Selection: water-resistant phosphorus nitrogen boron composite+nano SiO ₂ reinforcement, low moisture absorption, high carbonization, and hydrophobic carbon layer.
-Requirements: 240h water resistance, fire resistance limit ≥ 3h, coating no cracking, adhesion ≥ 2MPa.
-Selection: Fully hydrophobic modified expansion flame retardant system+self-healing microcapsules, zero precipitation, immersion resistance, non hydrolysis of carbon layer.
-Requirements: Soak for 168 hours without precipitation, flame retardant without degradation, and waterproof and mildew resistant coating.
-Selection: Low ion migration water-resistant flame retardant+epoxy modified system, high insulation performance retention, no leakage risk.
-Requirement: Volume resistivity ≥ 10 ¹⁶Ω· cm, insulation retention ≥ 90% after immersion in water.
1. Only focus on initial flame retardancy and ignore moisture retention rate: initial V-0 ≠ long-term reliability, and immersion degradation is the most common failure.
2. Simple modification of ordinary apps for water resistance: Low polymerization apps can still hydrolyze under long-term humidity, requiring dual protection of high polymerization and microcapsule encapsulation.
3. The higher the amount added, the better: Excessive addition reduces compatibility and exacerbates interfacial water absorption, requiring the optimal ratio.
4. Neglecting hydrophobicity and interface treatment: Without compatibility/hydrophobic modification, water resistance cannot be discussed.
-EU: RoHS, REACH, halogen-free, low VOC
-North America: UL94, ASTM D2863, UL 1581
-China: GB14907, GB28374
-International: IEC 60695, ISO 5660
Against the backdrop of rapidly increasing demand for engineering construction in humid regions around the world, water resistance is no longer a bonus, but a necessary threshold for fire-resistant coatings and flame retardants to enter the high-end market. Scientific selection requires comprehensive evaluation from five dimensions: component structure, water resistance testing, performance retention, scenario matching, and global compliance, rather than just looking at initial flame retardant data.
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