Behind every dazzling screen and deep in the center console of every smart car, there is a crucial material that is almost imperceptible to the naked eye - optical grade highly transparent liquid adhesive, known as LOCA (Liquid Optically Clear Adhesive) in the industry. It is colorless and transparent, with a light transmittance of over 99% after curing, and a haze as low as 0.1% or even 0.0015%, like a layer of disappearing air. However, it firmly welds glass and glass, glass and plastic together, allowing light to freely shuttle and allowing images to be fully displayed. This is not a prop in science fiction movies, but one of the most essential bonding solutions in the current display and optical industries.

The essence of this material is a liquid special adhesive that has been precisely molecular designed. The basic polymer is often made of acrylic or organosilicon systems, combined with reactive diluents, crosslinking agents, and photoinitiators, through strict proportioning and stirring processes. Taking a typical UV curing formula as an example, the proportion of liquid rubber acrylic monomers can reach 20% to 70%, active diluent monomers account for 20% to 60%, crosslinking monomers account for 3% to 20%, supplemented with polybutadiene resin and photoinitiator. The viscosity of the final product is controlled between 1000 and 4500 centipoise at 25 ℃, ensuring fluidity for easy dispensing and coating, and preventing overflow and contamination due to excessive dilution.

After curing, the refractive index of the adhesive layer is precisely tuned to between 1.48 and 1.52, highly matching with substrates such as glass, PMMA, PC, etc., thereby minimizing interface reflection and light scattering losses. Actual test data shows that excellent LOCA products have a shear strength of 3.8 to 4.2 MPa, a fracture elongation of 170% to 212%, and a Shore hardness of only 12A to 25A. They are soft and tough, like putting an elastic armor on optical components. What is even more commendable is its resistance to yellowing, with a yellowing index that can be controlled below 0.4. Even after being exposed to 60 ℃ for 500 hours in a UV aging chamber, it remains clear as before.

The curing method of LOCA is flexible and versatile, with the most common being UV curing. After coating and bonding, it can be initially cured in seconds to tens of seconds by being irradiated with UV light at 365nm or 395nm wavelengths, making it highly efficient and suitable for automated production lines. However, UV curing has a natural weakness - shaded areas cannot be illuminated. Therefore, the industry has developed technology routes such as UV and heat dual curing, UV and moisture dual curing, etc. The LOCA of the organic silicon system achieves a balance between room temperature curing and extremely low shrinkage rate, with a curing shrinkage rate that can be reduced to below 0.1%, far exceeding the industrial standard requirement of 2.5%. This low shrinkage characteristic means that the adhesive layer will not generate stress due to volume changes, avoiding a series of fatal defects such as shrinkage, fracture, optical deformation, etc.

Regarding liquid silicone rubber, please refer to our website for details: IOTA Liquid Silicone Rubber