Maintaining bond strength and optical transmittance in hot and humid environments primarily relies on the heat- and humidity-resistant formulation of both the substrate and adhesive, protecting the material from environmental influences at its source. The substrate for this type of OCA is typically a highly hydrolysis-resistant polymer resin. This resin's stable molecular chain structure makes it less susceptible to chemical reactions with water molecules, leading to chain breakage under high temperature and humidity conditions. This prevents deformation and cracking of the substrate due to hydrolysis, thereby maintaining uniform optical transmittance. Hydrolysis failure of the substrate not only results in optical transmittance defects due to structural damage but also directly impacts the bond stability with the adhesive layer. Furthermore, the adhesive eliminates small molecules that are prone to moisture absorption and instead utilizes a low-hydrophilic, long-lasting polymer adhesive system. This minimizes bond loss due to moisture absorption, even in high moisture content, ensuring a secure bond between the OCA and the substrate (such as glass or display panel).
Optimizing the cross-linking structure is crucial for maintaining OCA performance in hot and humid environments. Increasing the cross-linking density enhances moisture and heat resistance. The adhesive layer of OCA utilizes a multifunctional crosslinker to form a three-dimensional network structure. This structure significantly reduces the rate and extent of water permeation. The tightly bound crosslinked network acts as a barrier, reducing the possibility of water vapor entering the adhesive and substrate interface, thereby preventing interfacial separation and bonding failure caused by water vapor intrusion. Furthermore, a suitable crosslinking degree enhances the adhesive's stability in high temperatures and humidity while maintaining its flexibility. Even in long-term hot and humid environments, the adhesive strength does not weaken due to loosening of the crosslinking structure. Furthermore, the three-dimensional network structure is less susceptible to molecular chain displacement, maintaining uniform optical transmission of the optical adhesive and preventing issues such as light scattering and reduced transmittance due to structural changes.
The interface treatment between the OCA and the substrate strengthens the bond stability and resists damage from hot and humid environments. Before lamination, the OCA's bonding surface and the substrate's surface undergo specialized treatment. For example, plasma cleaning technology is used to remove surface oil and impurities while increasing surface active groups. In some scenarios, a moisture- and heat-resistant coupling agent is introduced at the interface. This agent forms a "bridge" between the OCA and the substrate, enhancing their chemical and physical adhesion. This treated interface reduces moisture accumulation in hot and humid environments, preventing debonding caused by moisture permeation. It also minimizes light reflection and scattering at the interface, ensuring that light transmission is unaffected by changes in the interface state. This creates a stable, integrated structure between the OCA and the substrate, maintaining both bonding strength and optical quality.
The moisture-resistant encapsulation and edge protection design block moisture intrusion from the outside, helping the OCA maintain its core performance. In practical applications, after OCA optical adhesive lamination is completed, the edges of the display module are sealed with a moisture- and heat-resistant sealant. This prevents moisture from seeping through the edges and into the OCA and the lamination interface. Edges are a primary route for moisture intrusion. Without protection, moisture can easily penetrate along these edges in humid and hot environments, leading to localized adhesion loss and uneven light transmission. This encapsulation design not only reduces the impact of moisture on the OCA itself but also protects the interface between the OCA and the substrate, preventing delamination and warping at the edges. This maintains overall lamination stability and consistent light transmission, making it particularly suitable for use in environments with high humidity, heat, or moisture, such as bathrooms, kitchens, and vehicles.
The anti-aging and optical stabilizing ingredients added to OCA optical adhesive inhibit performance degradation in humid and hot environments, ensuring long-term stable light transmission. Humid and hot environments can accelerate material aging, causing yellowing and reduced light transmittance in OCAs. Therefore, antioxidants, UV absorbers (which can inhibit thermal oxidative aging even in hot and humid environments without direct sunlight), and anti-yellowing agents are incorporated into the formulation. These additives capture free radicals generated in hot and humid environments, preventing them from damaging the OCA's molecular structure and reducing aging-related yellowing. Furthermore, the additives are evenly dispersed within the OCA, preventing the formation of light scattering centers and the impact of added ingredients on light transmittance. This ensures that the OCA maintains its high light transmittance and low haze optical properties even in long-term hot and humid conditions, without compromising display panel image quality.
A dynamic bonding adjustment mechanism allows the OCA to autonomously maintain bonding strength despite slight performance fluctuations in hot and humid environments. Some high-end OCA optical adhesives feature dynamic cross-linking. Under hot and humid conditions, the molecular chains in their adhesive layer can "self-repair" through subtle molecular motion. If environmental changes cause a slight drop in localized adhesion, the molecular chains can re-adjust their bond, strengthening the local bond. This dynamic property does not disrupt the overall cross-linking structure or affect light transmission. Furthermore, the interface between the OCA substrate and adhesive layer is designed with a gradient transition structure to avoid interfacial stress concentration caused by differences in thermal expansion coefficients under hot and humid conditions, minimizing stress damage to the bond and ensuring a stable bond between the OCA and the substrate despite temperature and humidity fluctuations.
Optimized for applications in hot and humid environments, OCA's performance stability is further enhanced through process and structural adjustments. During the production process, OCA formulation parameters are adjusted based on the humidity and heat levels of the target application scenario (e.g., tropical regions, high-humidity industrial environments). For example, the amount of crosslinker is increased in high-humidity environments, and a more hydrolysis-resistant substrate is selected. The lamination process is also optimized, using vacuum lamination technology to reduce residual bubbles between the OCA and the substrate. The air inside these bubbles tends to expand in hot and humid environments, which not only affects light transmittance but can also squeeze the OCA, causing localized debonding. Furthermore, some OCAs are designed with a "thin, high-adhesion" structure. While maintaining light transmittance, this structure reduces the thickness to shorten the water vapor permeation path, minimizing the impact of moisture on overall performance. This ensures that the bonding strength and light transmittance consistently meet the requirements in specific hot and humid environments.
