FAQ

1. The Core Causes of Natural Aging in Powder Coatings

Powder coatings, widely used in industrial corrosion prevention and architectural decoration, are environmentally friendly coatings whose service life and weather resistance directly affect their usability. In the natural environment, the aging and degradation of powder coatings is the result of multiple factors. Ultraviolet radiation is the main driving factor for natural aging, while atmospheric oxygen is a key auxiliary factor promoting the continued aging reaction. Ultraviolet radiation, as a high-energy electromagnetic wave, can penetrate the surface film of powder coatings and act on the polymer molecular chains. When the ultraviolet energy reaches the bond energy threshold of the polymer molecular chains, it triggers the breakage and recombination of the molecular chains, initiating the auto-oxidation reaction of the powder coating, commonly known as the oxidation chain reaction. This reaction leads to the destruction of the structural integrity of the polymer molecules, thus causing the coating to degrade. It is worth noting that water and heat in the environment significantly accelerate this oxidation chain reaction, playing a strong photo-oxidation promoting role—the presence of moisture reduces the bond energy stability of the polymer molecular chains, while heat provides additional activation energy for the reaction, allowing the oxidation degradation reaction to occur at a lower energy threshold, significantly shortening the aging cycle of the powder coating.

2. Specific Manifestations and Intrinsic Mechanisms of Powder Coating Film Aging

During the production and preparation of powder coatings, due to the complexity of the formulation and subtle differences in processing technology, the resulting coating film inevitably contains weak bonds and diene-structured macromolecular chains. These structures are inherently unstable and easily undergo photo-induced oxidative degradation reactions under continuous ultraviolet radiation. This process is the core intrinsic mechanism of coating film aging. As the photo-oxidative degradation reaction continues, the powder coating film exhibits a series of obvious performance degradation phenomena: First, fading occurs because the breakage of polymer molecular chains damages the pigment coloring system in the coating, leading to decreased color saturation and even discoloration; second, chalking occurs because the degraded polymer molecules gradually lose their binding force and detach from the coating surface as powder, gradually thinning the coating and causing it to lose its original protective and decorative functions. Furthermore, when powder coatings are subjected to high-temperature baking (such as secondary heating after curing in industrial production, or high-temperature outdoor environments) or prolonged exposure to sunlight, thermo-oxidative degradation can occur, manifesting as yellowing, embrittlement, and cracking of the coating film. These aging phenomena not only severely affect the product’s appearance but also lead to a significant decrease in key properties such as adhesion, hardness, and corrosion resistance, directly impacting the service life and safety of the coated product.

3. Mechanism of Action and Application Value of Antioxidants in Powder Coatings

To inhibit or reduce the thermo-oxidative degradation of powder coatings and slow down the aging process, the industry commonly adopts the technical solution of adding antioxidants or heat stabilizers to the coating formulation. Among these, antioxidants are the most widely used and have the most significant effects. The mechanism of action of antioxidants in powder coatings is mainly reflected in two aspects: Firstly, antioxidants can capture free radicals generated in the oxidation chain reaction, interrupting the chain transmission of the oxidation reaction and inhibiting the degradation of polymer molecules from the source; secondly, antioxidants can decompose peroxides generated in the oxidation reaction, preventing peroxides from further causing molecular chain breakage, thereby protecting the structural integrity of the polymer molecular chain. From a practical application perspective, adding antioxidants to powder coating formulations can significantly increase the pigment-to-binder ratio (the ratio of pigment to resin). While achieving the same performance indicators as with a lower pigment-to-binder ratio when no antioxidant is added, it effectively reduces the amount of resin used, optimizing formulation costs. The core reason for this advantage is that the addition of antioxidants reduces the tendency of resin to decompose into low-molecular-weight products during processing, storage, and use. This allows macromolecular resins to more stably coat more fillers (such as pigments and extender pigments), achieving optimized pigment-to-binder ratios in the formulation without affecting key properties such as film density and adhesion, bringing significant economic benefits to enterprises.

4. Advantages and Dosage Control of Light Stabilizers in Powder Coatings

Due to the diverse and complex characteristics of powder coating formulations (e.g., epoxy, polyester, polyurethane), curing processes (high-temperature curing, low-temperature curing, UV curing), and curing methods (e.g., electrostatic spraying curing, fluidized bed dip coating curing), powder coatings face significantly different photoaging pressures in different application scenarios. Therefore, photocuring and photoprotection are crucial for ensuring the service life of powder coatings. Light stabilizers, as additives specifically designed for photoaging, have a different mechanism of action than antioxidants. They primarily prevent UV damage to polymer molecular chains by absorbing ultraviolet light, quenching excited-state molecules, or capturing free radicals. Practice has proven that light stabilizers are highly effective in improving the photoaging resistance of coatings and extending their service life, with the significant advantages of low dosage and high efficiency—generally, the amount of light stabilizer added is only 0.5% to 1.0% of the total formulation to achieve significant anti-photoaging effects. In contrast, achieving photoaging resistance by adjusting resin type or increasing coating thickness is not only more expensive but may also affect the coating’s application performance and appearance. Therefore, the rational application of light stabilizers in powder coatings has become a simple, low-cost, and highly effective method to improve their weather resistance, and is widely used in the formulation design of outdoor powder coatings (such as architectural aluminum profiles, outdoor furniture, and transportation facilities).

5. Synergistic Effects and Potential Risks of Combining Antioxidants and Light Stabilizers

As mentioned earlier, light stabilizers and antioxidants have fundamentally different stabilization mechanisms for coatings: antioxidants mainly target thermo-oxidative degradation, focusing on inhibiting the oxidative chain reaction; light stabilizers mainly target photo-oxidative degradation, focusing on blocking ultraviolet radiation from damaging the molecular chains. Theoretically, combining these two stabilizers with different mechanisms of action can achieve a synergistic effect of “1+1>2.” that is, through complementary effects, comprehensively covering the thermo-oxidative and photo-oxidative aging risks faced by powder coatings during use, further improving the overall stability of the coating film. However, in practical applications, the combined effect of two stabilizers is not always synergistic; additive or antagonistic effects may occur. An additive effect means the combined effect of the two stabilizers is only equal to the sum of their individual effects, failing to improve performance. An antagonistic effect is even more detrimental; the two stabilizers may react chemically or interfere with each other’s mechanisms of action, resulting in a lower stabilizing effect when used together than when either is used alone, thus reducing the stability of the coating film. The reasons for this difference are mainly related to factors such as the type of stabilizer, the addition ratio, the powder coating formulation, and the application environment. For example, when certain phenolic antioxidants are used in combination with specific types of light stabilizers, a redox reaction may occur, leading to the consumption of the effective components of both. Furthermore, the interaction strength between stabilizers varies with different addition ratios; a synergistic effect can only be achieved within a suitable ratio range. Therefore, when antioxidants and light stabilizers are used in combination, a thorough understanding of their chemical reaction characteristics is crucial. Only by accurately grasping the potential chemical mechanisms underlying their combined effects can the optimal combined system be determined through experimental optimization. This includes the selection of stabilizer types and adjustments to the addition ratio, thereby avoiding antagonistic effects and maximizing synergistic effects.

6. Practical Verification of the Combined Effects of Antioxidants and Light Stabilizers

Numerous experimental studies and industrial application cases show that the combined application of light stabilizers and antioxidants in high-performance powder coatings exhibits significantly different effects. The key lies in the rationality of the application method: When selecting a highly compatible stabilizer type, controlling the optimal addition ratio, and making targeted adjustments to the powder coating formulation system, a synergistic effect can be successfully achieved. For example, in outdoor polyester powder coatings, using hindered amine light stabilizers (HALS) and phosphite antioxidants in appropriate proportions allows HALS to effectively capture free radicals generated by photo-oxidation, while phosphite antioxidants decompose peroxides. This synergistic effect improves the coating’s weather resistance (e.g., resistance to accelerated aging) by more than 30% compared to using either stabilizer alone, significantly extending the product’s lifespan in outdoor environments. Conversely, if the stabilizer type is improperly selected, the addition ratio is unbalanced, or the formulation characteristics of the powder coating (e.g., resin type, pigment type) are not fully considered, additive or even antagonistic effects can easily occur. For instance, in epoxy powder coatings, using certain thioester antioxidants and benzophenone light stabilizers together may lead to problems such as haze and accelerated yellowing due to their chemical incompatibility, while failing to effectively improve aging resistance.

7. Summary

The problems of moisture-induced fogging and aging in powder coatings (such as fading, chalking, and yellowing) are essentially the result of oxidative degradation of polymer molecular chains under the combined effects of environmental factors such as ultraviolet radiation, oxygen, water, and heat. The presence of weak bonds and diene structures is an inherent cause of easy aging of the coating film. Antioxidants and light stabilizers, as two core anti-aging additives, act against thermo-oxidative degradation and photo-oxidative degradation respectively, and are key means to improve the stability of powder coatings. Antioxidants can reduce resin degradation and optimize the pigment-to-binder ratio by inhibiting oxidative chain reactions; light stabilizers achieve highly effective anti-photoaging with low dosage, extending the service life of the coating film. When both are used together, if their chemical reaction mechanisms are fully understood, and the types and addition ratios are rationally selected and adjusted, a synergistic effect can be achieved, significantly improving the weather resistance of the coating film; however, improper use may result in additive or antagonistic effects, affecting product performance. Therefore, in the formulation design and application of powder coatings, it is necessary to scientifically select anti-aging stabilizers and optimize their application schemes, taking into account the specific usage environment, formulation system, and performance requirements. Only in this way can the problems of moisture absorption, fogging, and aging be fundamentally solved, ensuring the long-term stable performance of powder coatings and providing strong support for improving the quality of related products.