Optical Film Composition Balancing Stiffness and Flexibility
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Solution Overview
Problem
Existing optical films lack sufficient Shore D hardness, tensile modulus, and puncture strength, making them susceptible to deformation or breakage under external forces, which is a challenge for their use as cover windows or TFT substrates in display devices.
Innovation Solution
The optical film is formulated with a Stiff Index (STI) of 80 to 190, comprising a Shore D hardness of 15 to 19 HD and a tensile modulus of 5.0 to 10.0 GPa, achieved through a polymerizable composition containing diamine and dianhydride compounds, with specific ratios of imide and amide repeating units, and controlled molar ratios of dianhydride and dicarbonyl compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the optical film is made thinner to reduce weight and increase flexibility, then the flexibility and weight are improved, but the mechanical strength and stiffness deteriorate
Solution Approach 1:
The patent changes the chemical composition parameters of the polymer by controlling the molar ratios of diamine monomers (TFDB, 3DDS, 4DDS) and the ratio of imide to amide repeating units. This compositional parameter adjustment achieves optimal balance between flexibility and mechanical strength, with imide:amide ratios of 10:90 to 2:98 providing sufficient stiffness while maintaining flexibility for thin-film applications.
Solution Approach 2:
The patent creates a composite polymer structure combining imide and amide repeating units in specific ratios within the same polymer chain. This composite approach at the molecular level allows the material to exhibit both the flexibility needed for thin films and the mechanical strength required for structural applications in display devices.
2Adaptability or versatility
If the optical film is made thinner to increase flexibility, then the flexibility is improved, but the puncture strength deteriorates
Solution Approach 1:
The patent adjusts the chemical composition parameters by controlling the content of TFDB (70-80 mol%) and sulfone diamines (20-30 mol%), which directly affects the polymer's resistance to puncture. The specific monomer composition creates a polymer structure that maintains high puncture strength even at reduced thickness, enabling flexible yet durable optical films.
3Strength
If the Shore D hardness is increased to improve surface stiffness, then the surface stiffness is improved, but the overall mechanical flexibility deteriorates
Solution Approach 1:
The patent precisely controls the imide to amide repeating unit ratio (10:90 to 2:98) to adjust the Shore D hardness to the optimal range of 15-19 HD. This parameter optimization ensures the surface has sufficient stiffness for display applications while the overall film maintains the flexibility needed for conformal mounting and bending applications.
Solution Approach 2:
The patent creates local quality differentiation within the polymer structure by having imide repeating units provide localized surface stiffness and hardness, while the amide repeating units maintain overall film flexibility. This spatial distribution of different functional units within the polymer chain resolves the contradiction between surface stiffness and bulk flexibility.
Data Source
AI summary
An embodiment of the present invention provides an optical film which has a stiffness index (STI) of 80 to 190, based on a thickness of 50 μm. The Stiff Index is calculated by expression 1 below: [Expression 1] STI=Shore D hardness×tensile modulus. In expression 1, “STI” denotes a stiffness index, the Shore D hardness is a hardness measured using a Shore D durometer, and the tensile modulus is a tensile modulus measured using a universal testing machine.