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Home / News / Industry News / Plastic Coating Develops Yellowing and Softening at High Temperature — How to Improve?
Industry News
Plastic Coatings · Consumer Electronics · Home Appliances · Daily Products
Plastic substrate coatings readily develop yellowing, softening, and peeling in high-temperature environments, making it difficult to adapt to multi-scenario use requirements. Conventional plastic coatings, limited by the resin structure, formulation system, and cure process, readily develop surface deformation, colour change, and film peeling problems when facing temperature fluctuation and locally high-temperature environments. These problems significantly affect the appearance quality and service life of plastic products and are a long-standing common difficulty in the plastic coating industry.
Four Pain Points of Insufficient High-Temperature Resistance
1
Colour Change in High-Temperature Environments
Ordinary plastic coating pigments and resin systems have limited heat resistance. After temperature rises, internal organic components easily undergo structural changes, causing the film to develop yellowing, colour loss, and colour inconsistency.
2
Film Structure Softening and Deformation at High Temperature
Conventional coating cured molecular structure has weak stability — after heating, molecular chain activity increases, film hardness declines, and the surface readily develops softening, tackiness, and slight deformation.
3
Hot-Cold Cycling Causes Lifting and Peeling
The thermal expansion coefficients of plastic substrate and ordinary coating differ. During repeated temperature change, the inconsistent contraction rhythm of substrate and film generates internal stress — gradually causing film lifting, delamination, and peeling.
4
Weak High-Temperature Weathering Performance
High-temperature environments accelerate the ageing process of coating components, combined with the influence of various media in the air environment — the film readily develops chalking, cracking, and other ageing problems.
Three Paths to Optimise High-Temperature Resistance
Traditional optimisation approaches have prominent limitations — simply replacing expensive heat-resistant raw materials greatly increases production costs, while some high-heat-resistance resins have poor compatibility with plastic substrates, easily causing adhesion decline and leveling deterioration. Adjusting baking temperature alone can cause plastic deformation and embrittlement. A more effective approach addresses formulation, additives, and process simultaneously.
Formulation System Optimisation
Replace modified resin systems compatible with plastic substrates, selecting resin raw materials with stable molecular structures to improve the structural stability of the formed film. Simultaneously replace high-heat-resistance pigments and fillers to avoid pigment decomposition and colour change at high temperature.
Additive Matching
Appropriately add heat-resistant stabiliser additives to reduce ageing and cracking of the resin molecule at high temperature, reducing film yellowing and chalking. Match appropriate crosslinking additives to improve film crosslink density, making the cured film structure more dense — enhancing high-temperature resistance while maintaining flexibility to avoid hot-cold cycling delamination.
Coating Process Optimisation
Adjust the standardised cure process — after spraying, allow sufficient ambient-temperature flash drying time for gradual solvent evaporation, avoiding rapid evaporation of internal components during high-temperature baking causing film structure defects. Rationally control baking temperature and duration within the plastic substrate's tolerance range to ensure full film crosslinking.
Improving plastic coating high-temperature resistance performance cannot rely on any single adjustment. Comprehensively optimising the resin formulation, additive matching, and cure process together can progressively improve film colour stability, structural stability, and adhesion durability at high temperature — enabling the coating to maintain a stable surface state across a wider range of temperature variation environments.
Frequently Asked Questions
What is the maximum continuous service temperature of a typical 2K PU plastic coating before thermal degradation becomes visible?
Standard 2K PU plastic coatings typically show thermal degradation effects above 80–100°C with extended exposure. Yellowing in aromatic isocyanate-based systems begins at the lower end of this range. Aliphatic isocyanate systems with good UV and heat stabiliser packages can typically withstand 100–120°C for moderate exposure durations without obvious colour change or structural degradation. For applications regularly exposed above 120°C, specialised heat-resistant resins and pigment systems are required, and the specific temperature tolerance should be verified by accelerated heat ageing testing at the target conditions.
Does increasing crosslink density always improve hot-cold cycling resistance?
Not always. Higher crosslink density typically improves resistance to high-temperature softening, but a very highly crosslinked film has lower elongation at break and less ability to accommodate dimensional change during temperature cycling. This creates a trade-off: higher crosslink density for heat resistance can increase the tendency for interfacial stress cracking during rapid cold-hot cycling. For plastic substrates with significant thermal expansion, a moderate crosslink density that balances heat resistance with sufficient film flexibility is usually more durable in cycling conditions than a very high crosslink density.
