Flexible Window Film Buffer Layer for Rainbow Mura and Flexural Reliability

The patent applies composite materials by forming a buffer layer between the base layer and the functional coating layer. This buffer layer has a modulus of elasticity between 1/10 to 1/50 of the base layer's modulus, creating a gradient structure that combines the hardness needed for impact resistance with the flexibility needed for low-temperature flexural reliability. The composite structure allows the hard coating to protect against impact while the softer buffer layer prevents cracking during folding at low temperatures.

The patent changes the physical parameter of modulus of elasticity by creating a buffer layer with specifically controlled elastic modulus (1/10 to 1/50 of the base layer). This parameter change enables the window film to maintain both hardness for impact resistance and softness for flexural reliability under low temperature conditions, resolving the contradiction between these two properties.

The buffer layer with intermediate modulus (1/10 to 1/50 of base layer) acts as a stress-absorbing interface that prevents crack propagation during repeated folding. This composite structure maintains flexural reliability under high temperature and high humidity conditions while enabling the window film to be folded hundreds of thousands of times for flexible display applications.

The buffer layer serves as a pre-designed cushioning layer that absorbs stress and prevents damage before cracking can occur during repeated folding. This beforehand cushioning mechanism ensures the window film maintains reliability under harsh environmental conditions (high temperature and humidity) while achieving the required flexibility for repeated folding.

The patent applies local quality by creating a buffer layer with specific optical properties (refractive index between 1/10 to 1/50 of the base layer) in the region where refractive index differences cause rainbow mura. This localized adjustment of optical quality eliminates the harmful visual effect while maintaining the flexural reliability benefits of the buffer layer structure.

The buffer layer acts as an intermediary layer between the base layer and functional coating layer, mediating the refractive index difference that causes rainbow mura. By having a refractive index between 1/10 to 1/50 of the base layer, the buffer layer gradually transitions the optical properties, preventing sudden refraction changes that create rainbow mura while still providing the mechanical cushioning needed for flexural reliability.