Polyimide Film Optical Transparency Birefringence Reduction
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Solution Overview
Problem
Polyimides used in electronic devices face limitations due to their amber color and birefringence, which affect optical transparency and display performance, making them unsuitable for certain applications like color filters and touch screen panels.
Innovation Solution
A polyamic acid with a specific repeat unit structure and a high-boiling aprotic solvent is used to create a polyimide film with improved optical transparency and reduced birefringence, suitable for use as a flexible replacement for glass in electronic devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional polyimides are used to maintain thermal stability and mechanical toughness, then desirable mechanical and thermal properties are achieved, but optical transparency deteriorates due to amber color and birefringence
Solution Approach 1:
The patent modifies the chemical structure parameters of polyimides by incorporating specific aromatic diamine residues with substituents (R1 and R2 groups) at controlled positions. This structural parameter change reduces the amber coloration and birefringence while maintaining the thermal stability and mechanical properties through the preserved polyimide backbone structure.
Solution Approach 2:
The patent creates a composite polyimide structure by combining different aromatic diamine residues (Formula II and other aromatic diamines) with tetracarboxylic acid components. This composite approach allows the material to exhibit both the desired optical transparency from the specific diamine structure and the thermal/mechanical stability from the polyimide framework.
2Strength
If polyimides are used as flexible replacement for glass in electronic displays, then mechanical flexibility and toughness are improved, but display performance deteriorates due to optical retardation from birefringence
Solution Approach 1:
The patent changes the molecular orientation parameters by designing a polyimide structure where polymer chains are less prone to planar orientation during film formation. The specific aromatic diamine structure with substituents creates steric hindrance that disrupts chain alignment, thereby reducing birefringence and optical retardation while maintaining mechanical toughness.
3Adaptability or versatility
If conventional polyimides are used in color filter and touch screen applications, then general structural requirements are met, but application suitability deteriorates due to amber color limiting optical clarity
Solution Approach 1:
The patent modifies the optical parameters of polyimides by controlling the substitution patterns (R1 and R2 groups) and their positions (a, b, c, d values) in the aromatic diamine structure. This precise parameter control adjusts the light absorption characteristics to reduce amber coloration, achieving the optical clarity required for color filter and touch screen applications.
Data Source
AI summary
Disclosed is a polyimide having a repeat unit structure of Formula IVIn Formula IV: Ra is the same or different at each occurrence and represents one or more tetracarboxylic acid component residues; and Rb is the same or different at each occurrence and represents one or more aromatic diamine residues. 30-100 mol % of Rb has Formula IIIn Formula II: R1 and R2 are the same or different at each occurrence and are halogen, alkyl, fluoroalkyl, silyl, alkoxy, fluoroalkoxy, or siloxy; a and b are the same or different and are an integer from 0-4; c and d are the same or different and are 1 or 2; and * indicates a point of attachment.