Examples of basic formulas for acrylic resin automotive coatings and recommendations for silane coupling agents
1. Primer formula
Main resin: thermoplastic acrylic resin (40-60%) or hydroxy acrylic resin (for two-component systems)
Crosslinker: isocyanate curing agent (such as HDI trimer, for two-component), amino resin (such as methyl etherified melamine resin, for baking varnish)
Pigment/filler: titanium dioxide, carbon black, barium sulfate, etc. (15-30%)
Solvent: xylene, butyl acetate, propylene glycol methyl ether acetate (PMA), etc. (20-30%)
Additives: leveling agent, dispersant, silane coupling agent
2. Topcoat/clearcoat formula
Main resin: hydroxy acrylic resin (50-70%)
Curing agent: aliphatic isocyanate (such as Desmodur N 3390) or amino resin
UV absorber: benzotriazole (such as Tinuvin 1130)
Light stabilizer: HALS (such as Tinuvin 292)
Rheological additive: fumed silica (such as Aerosil 200)
Additive: silane coupling agent
Recommended silane coupling agents for improving adhesion and scratch resistance
Silane coupling agents improve the adhesion between resin and substrate (such as metal, glass or primer) by forming chemical bonds, while enhancing the crosslinking density of the coating to improve scratch resistance. The following types are recommended:
1. Epoxy silane
Model: γ-glycidyloxypropyltrimethoxysilane (SF-S560)
Function: Improve adhesion to metals (such as aluminum and steel), enhance water resistance and chemical resistance.
Addition amount: 0.5-2% (based on resin solids).
2. Amino silane
Model: γ-aminopropyltriethoxysilane (SF-S550)
Function: Improve compatibility with inorganic fillers and enhance wet adhesion.
3. Methacryloyloxysilane
Model: γ-methacryloyloxypropyltrimethoxysilane (SF-S570)
Function: Especially suitable for free radical curing system, improving scratch resistance and hardness.
4. Mercaptosilane
Model: 3-Mercaptopropyltrimethoxysilane (SF-S590)
Function: Used in UV curing system to enhance wear resistance.
Application suggestions
1. Pretreatment: Silane coupling agent can be diluted and sprayed on the substrate (0.5-1% water/alcohol solution), or directly added to the coating.
2. Compatibility test: The stability of silane and resin system needs to be verified (to avoid gelation).
3. Compounding additives: Scratch resistance can be further improved by using nano-silica (such as Aerosil R812).
Precautions
Hydrolysis control: Silane needs to be hydrolyzed under acidic conditions (pH 4-5) to avoid premature condensation.
Storage: It needs to be sealed and moisture-proof to avoid failure.
The comprehensive performance of the coating can be significantly improved by rationally selecting silane coupling agents and optimizing the formula. In practical applications, it is recommended to determine the optimal addition ratio through orthogonal experiments.