Outdoor guardrail powder coating: in-depth analysis of anti-ultraviolet additives and long-term stability

As the boundary between buildings and landscapes, the coating of outdoor guardrails is directly exposed to the natural environment and needs to withstand a variety of tests:
Wind and rain: continuous rain and wind may cause wear, cracking, or even shedding of the coating surface.
Temperature changes: extreme temperature fluctuations, especially high temperatures in summer and severe cold in winter, will accelerate the aging process of the coating and affect its physical properties.
Ultraviolet radiation: Ultraviolet rays are one of the most destructive factors in the outdoor environment. They can penetrate the coating, destroy polymer chains, cause color fading, surface cracking, and reduce the overall performance of the coating.
Chemical corrosion: pollutants in the air, acid rain and other chemicals may corrode the coating and affect its durability.
Mechanical stress: As a safety protection facility, the guardrail needs to withstand mechanical stress such as human leaning and impact, and the coating needs to have sufficient toughness and strength.

Powder coating is a solid powder coating that is evenly covered on the surface of the substrate by electrostatic spraying or fluidized bed dipping, and melts and solidifies into a film at high temperature. Compared with traditional solvent-based coatings, powder coatings have the following significant advantages:
Environmental protection: Powder coatings do not contain solvents, and there is no VOCs (volatile organic compounds) emission during the coating process, which is environmentally friendly.
High efficiency: Powder coatings have high coating efficiency, can realize automated production, and greatly shorten the coating cycle.
Weather resistance: The coating formed by powder coatings has excellent weather resistance and can resist various environmental factors such as ultraviolet rays, rain, and temperature changes.
Economic efficiency: Due to the high coating efficiency and stable coating quality, the use cost of powder coatings is relatively low, and maintenance is simple, which reduces long-term operating costs.

In powder coatings, anti-UV additives are key components to ensure the long-term stability of the coating. It can not only effectively resist the damage of ultraviolet rays, but also improve the overall performance of the coating, which is specifically manifested in the following aspects:
Ultraviolet protection: Anti-UV additives can absorb or reflect ultraviolet energy, reduce its damage to the internal polymer chains of the coating, and prevent color fading and surface cracking.
Improved weather resistance: By reducing the destructive effect of ultraviolet rays, anti-UV additives significantly improve the weather resistance of the coating, enabling it to maintain stable performance under extreme climatic conditions.
Enhanced chemical corrosion resistance: UV-resistant additives can also improve the coating's resistance to chemicals and reduce the corrosion of acid rain, pollutants, etc. on the coating.
Improved mechanical strength: By enhancing the cross-linking degree of the polymer chain inside the coating, UV-resistant additives improve the toughness and strength of the coating, enabling it to better withstand mechanical stress.

UV-resistant additives can be divided into three categories according to their mechanism of action: absorption type, shielding type and reactive type:
Absorption type UV-resistant additives: This type of additive can absorb UV energy and convert it into harmless heat energy release, thereby protecting the coating from UV damage. Common absorption type UV-resistant additives include benzotriazoles, benzophenones, etc.
Shielding type UV-resistant additives: Through physical shielding, such as adding fine metal oxide particles (such as titanium dioxide, zinc oxide), reflect or scatter UV rays to reduce their penetration depth into the coating. This type of additive not only provides UV protection, but also gives the coating a certain color effect.
Reactive type UV-resistant additives: This type of additive can chemically bond with the polymer chain to form a stable structure and improve the light aging resistance of the coating. Reactive UV-resistant additives usually contain functional groups that can react with resin molecules, such as hydroxyl and amino groups.
In outdoor guardrail powder coatings, one or more UV-resistant additives are usually selected for compounding according to specific needs to achieve the best UV protection effect. For example, in coatings that require high transparency, absorbing UV-resistant additives may be selected; while in situations where the color and gloss of the coating need to be enhanced, shielding UV-resistant additives may be selected.

Take the iron guardrail in a city park as an example. The guardrail is coated with powder coatings with UV-resistant additives added. After two years of outdoor exposure testing, the guardrail coating performed well:
Color stability: The coating is bright in color and has no obvious fading. Compared with the new coating, the color difference is less than ΔE*ab=2, which is within the visual acceptance range.
Surface integrity: The coating surface is smooth and flat, without defects such as cracks and peeling, maintaining good appearance quality.
Weather resistance: The coating has withstood the test of extreme climatic conditions, such as high temperatures in summer and severe cold in winter, and has no obvious signs of aging.
Chemical corrosion resistance: Under severe weather conditions such as acid rain, the coating did not corrode or blister, maintaining good protective performance.
Mechanical strength: The coating did not break or fall off when subjected to mechanical stress such as human leaning and impact, proving its excellent mechanical properties.