As LED light strips gain popularity and expand in market capacity, selecting the appropriate sealing adhesive for LED flexible strips has become a significant challenge for many manufacturers. Currently, there are three main types of sealing adhesives available: epoxy, polyurethane, and silicone.
Firstly, epoxy resin sealing material is known for its superior light transmittance and stacking properties, which can enhance the brightness and roundness of cured LED soft light strips. However, it has some limitations; it operates effectively only within a temperature range of -50°C to 550°C. At higher temperatures, the toughness of epoxy tends to diminish. Once the temperature exceeds 600°C, the adhesive can soften, leading to an increased risk of cracking. Over time, slight movements can cause the adhesive to peel or fracture, especially after the light beads have been in use for 400 to 700 hours, during which the epoxy adhesive above the light beads may turn yellow-brown, resulting in diminished brightness and variations in color temperature.
On the other hand, polyurethane sealing material offers light transmittance of 85-92% and provides good flexibility once cured. This type of adhesive can function effectively in temperatures ranging from -250°C to 950°C. However, its hardness limits its application to gel-type or semi-sleeve flexible light strips. The flexibility of the light strip can change considerably at lower temperatures. Additionally, when applying this adhesive, proper attention must be given to the surface of the FPC and the surrounding humidity levels. Excessive humidity can lead to white fogging on the product’s surface and reduced adhesion. For outdoor applications, the polyurethane gel may yellow within 2-3 years.
Silicone resin sealing adhesive is the most widely used option in the market today. The cured gel’s hardness can be adjusted, allowing for use as either a soft gel or a firmer Shore A 30-degree gel. This adhesive is suitable for gel-type light strips, semi-tube light strips, and full-tube light strips. It maintains its performance across a temperature range of -45°C to 200°C, with minimal impact on its mechanical, physical, and optical properties under varying temperatures. This makes it an ideal choice for cold regions such as Russia, Northern Europe, and North America. Furthermore, silicone adhesive light strips boast excellent resistance to ozone, UV light, acids, and alkali, ensuring long-term use without the risk of yellowing.