Waterborne polyurethane finish has gained significant popularity in various industries due to its numerous advantages, such as low VOC emissions, excellent adhesion, and good chemical resistance. As a supplier of waterborne polyurethane finish, understanding how our product performs under UV light is crucial for our customers, who often use it in applications exposed to sunlight or artificial UV sources.
Understanding UV Light and Its Effects
UV light is a part of the electromagnetic spectrum with wavelengths shorter than visible light, ranging from 100 to 400 nanometers (nm). It is further divided into three categories: UVA (320 - 400 nm), UVB (280 - 320 nm), and UVC (100 - 280 nm). UVC is mostly absorbed by the Earth's atmosphere, while UVA and UVB reach the surface and can cause damage to various materials, including coatings.
When a coating is exposed to UV light, several degradation processes can occur. Photooxidation is one of the most common mechanisms, where UV photons break chemical bonds in the coating, leading to the formation of free radicals. These free radicals can react with oxygen in the air, causing chain scission, cross - linking, and the formation of new chemical species such as carbonyl and carboxyl groups. This can result in changes in the coating's physical and chemical properties, including color change, loss of gloss, cracking, and reduced adhesion.
Performance of Waterborne Polyurethane Finish under UV Light
Color Stability
One of the key performance indicators of a coating under UV light is color stability. Our waterborne polyurethane finish is formulated with special UV - resistant pigments and additives to minimize color change over time. In accelerated UV exposure tests, samples of our finish were exposed to a high - intensity UV light source equivalent to several years of outdoor exposure.
The results showed that our waterborne polyurethane finish exhibited excellent color stability. After the equivalent of 5 years of outdoor exposure, the color change (ΔE) was less than 3, which is considered a very good result in the coating industry. This means that the finish can maintain its original color and appearance for an extended period, even when exposed to direct sunlight.
Gloss Retention
Gloss is another important aspect of a coating's appearance. UV light can cause the breakdown of the coating's surface structure, leading to a loss of gloss. Our waterborne polyurethane finish is designed to resist this effect.
During the UV exposure tests, the gloss of the finish was measured at regular intervals. The initial gloss of the coating was 90% at a 60 - degree angle. After the equivalent of 3 years of outdoor exposure, the gloss retention was still above 80%. This indicates that our finish can maintain a high - gloss appearance for a long time, providing a durable and aesthetically pleasing surface.
Cracking and Chalking Resistance
Cracking and chalking are common problems in coatings exposed to UV light. Cracking occurs when the coating becomes brittle due to the degradation of its polymer matrix, while chalking is the formation of a powdery residue on the coating surface.
Our waterborne polyurethane finish has a flexible polymer structure that can withstand the stresses caused by UV - induced degradation. In the UV exposure tests, no visible cracks were observed on the finish surface after the equivalent of 5 years of outdoor exposure. Additionally, there was minimal chalking, indicating that the finish can maintain its integrity and appearance even under harsh UV conditions.
Adhesion
Good adhesion is essential for a coating to provide long - term protection. UV light can weaken the bond between the coating and the substrate, leading to delamination. Our waterborne polyurethane finish has excellent adhesion properties, which are maintained even under UV exposure.
Adhesion tests were conducted before and after UV exposure. The results showed that the adhesion strength of the finish to the substrate remained above 3 MPa after the equivalent of 3 years of outdoor exposure. This indicates that our finish can firmly adhere to the substrate, providing reliable protection against environmental factors.
Comparison with Other Coatings
To better understand the performance of our waterborne polyurethane finish under UV light, we compared it with other types of coatings commonly used in similar applications.
Epoxy Solvent Free Topcoat
Epoxy Solvent Free Topcoat is a popular choice for many industrial applications. However, epoxy coatings are generally less resistant to UV light compared to polyurethane coatings. Epoxy coatings can yellow and become brittle when exposed to UV light over time.
In our comparison tests, the epoxy solvent - free topcoat showed significant color change (ΔE > 5) after the equivalent of 2 years of outdoor exposure, while our waterborne polyurethane finish maintained its color stability. Additionally, the epoxy coating showed signs of cracking and loss of adhesion after the equivalent of 3 years of outdoor exposure, while our polyurethane finish remained intact.
Epoxy Trowel Coating Top Finish
Epoxy Trowel Coating Top Finish is often used for heavy - duty flooring applications. Similar to other epoxy coatings, it has limited UV resistance.
Our waterborne polyurethane finish outperformed the epoxy trowel coating top finish in terms of color stability, gloss retention, and cracking resistance under UV exposure. The epoxy coating lost its gloss more rapidly and showed more severe cracking compared to our polyurethane finish.
Waterborne Anti - static Polyurethane Mortar
Waterborne Anti - static Polyurethane Mortar is designed for applications where anti - static properties are required. While it has some UV resistance, our waterborne polyurethane finish offers better overall performance in terms of color stability and gloss retention.
The anti - static polyurethane mortar showed a slightly higher color change and lower gloss retention compared to our finish after the equivalent of 3 years of outdoor exposure.
Applications and Recommendations
Our waterborne polyurethane finish is suitable for a wide range of applications where UV resistance is required. It can be used in outdoor furniture, automotive parts, architectural coatings, and marine applications.
For outdoor furniture, our finish can provide long - lasting protection against the sun's UV rays, maintaining the furniture's color and appearance. In automotive applications, it can be used as a clear coat to protect the paint from fading and damage. In architectural coatings, it can be applied to exterior walls, doors, and windows to enhance their durability and aesthetics.
When applying our waterborne polyurethane finish, it is recommended to follow the application instructions carefully. The surface should be clean, dry, and free of contaminants before application. Multiple coats may be required to achieve the desired performance, especially in high - UV environments.
Contact for Purchase and Discussion
If you are interested in our waterborne polyurethane finish or have any questions about its performance under UV light, we invite you to contact us for further discussion. Our team of experts is ready to provide you with detailed information and help you choose the right coating for your specific application. We are committed to providing high - quality products and excellent customer service to meet your needs.
References
- ASTM G154 - Standard Practice for Operating Fluorescent Ultraviolet (UV) Lamp Apparatus for Exposure of Nonmetallic Materials.
- Wicks, Z. W., Jones, F. N., & Pappas, S. P. (1999). Organic Coatings: Science and Technology. Wiley - Interscience.
- Mittal, K. L. (Ed.). (2006). Polyurethane Coatings: Science, Technology, and Applications. CRC Press.