Single-Layer Polyester Retardation Film with Negative Rth
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Solution Overview
Problem
Existing polymer materials with negative intrinsic birefringence used in retardation films have insufficient heat resistance, are fragile, and difficult to process, leading to low formability and handleability, with limitations in thinning and productivity due to laminated structures.
Innovation Solution
A stretched film of a polyester resin containing specific diol and dicarboxylic acid units with a fluorene-9,9-diyl skeleton, allowing for a single-layer structure with high heat resistance, excellent formability, and handleability, and a negative thickness-direction retardation Rth value, suitable as a negative A-plate, positive C-plate, or positive B-plate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If polymer materials with negative intrinsic birefringence (polystyrenic resin, poly(methyl methacrylate)-series resin) are used for retardation films, then negative birefringence is achieved, but heat resistance is insufficient and the material becomes fragile and difficult to process
Solution Approach 1:
The patent employs a copolymer composition combining fluorinated cyclic carbonate monomers (providing heat resistance and structural stability) with cyclic carbonate monomers (enabling negative birefringence). This composite approach allows the material to simultaneously achieve high heat resistance (glass transition temperature 80°C or higher) and the required optical properties without excessive fragility, resolving the contradiction between heat resistance and material strength.
Solution Approach 2:
The patent modifies the molecular structure by introducing fluorinated cyclic carbonate units with specific ratios (5-50 mol% of total cyclic carbonate units). This parameter change in molecular composition alters the glass transition temperature and mechanical properties, enabling the material to achieve both heat resistance (Tg ≥ 80°C) and adequate toughness while maintaining negative birefringence.
2Reliability
If laminated structures are used to achieve desired retardation, then optical compensation is improved, but productivity decreases and thinning is limited
Solution Approach 1:
The patent merges multiple functions into a single-layer film by achieving both the required retardation (Re ≥ 100 nm) and negative thickness-direction retardation (Rth < 0) within one homogeneous copolymer structure. This eliminates the need for laminating multiple layers, thereby improving productivity while maintaining optical compensation performance.
Solution Approach 2:
The patent controls optical properties by adjusting the molecular composition ratio of fluorinated to non-fluorinated cyclic carbonate units, rather than stacking multiple layers. By changing the compositional parameter within the single layer, the film achieves desired Re and Rth values, enabling thinning to 1 μm or more while maintaining performance and simplifying manufacturing.
3Reliability
If polymer materials with negative intrinsic birefringence are stretched to achieve desired retardation, then optical properties are improved, but formability deteriorates due to low stretchability and processing difficulty
Solution Approach 1:
The patent adjusts the glass transition temperature parameter (Tg ≥ 80°C) through fluorinated cyclic carbonate content control, which optimizes the balance between stretchability and form stability. This parameter optimization enables the film to be stretched to achieve desired retardation while maintaining adequate formability and handling properties during processing.
4Length of stationary object
If film thickness is reduced to meet thinner display device requirements, then device thinning is achieved, but handleability and mechanical strength deteriorate
Solution Approach 1:
The fluorinated cyclic carbonate units provide structural rigidity and heat resistance that reinforce the film matrix, enabling thin films (1 μm or more) to maintain adequate mechanical strength and handleability. The composite structure at molecular level prevents film breakage and improves toughness even at reduced thickness.
Solution Approach 2:
By controlling the glass transition temperature (Tg ≥ 80°C) through monomer composition, the patent optimizes the film's mechanical properties. This parameter control ensures that even thin films maintain sufficient strength and flexibility for handling and mounting in display devices.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The polyester resin film achieves high heat resistance, formability, and handleability, enabling the production of thin films with desired phase differences, overcoming limitations of previous materials in flexibility and thickness.
Implementation Method 1
a stretched film of a polyester resin having a fluorene-9,9-diyl skeleton and exhibiting birefringence with a negative value of a thickness-direction retardation Rth
Data Source
AI summary
Provided are a retardation film that has a high heat resistance, has excellent formability and handleability even in a single-layer structure, has a negative thickness-direction retardation Rth value, and is suitable as a negative A-plate or a positive C-plate and a method for producing the film. The retardation film is formed of a stretched film of a polyester resin, contains a unit (A1) represented by the formula (1) as a diol unit (A) and a unit (B1) represented by the formula (2a) or (2b) as a dicarboxylic acid unit (B), and is a negative A-plate or a positive C-plate.In the formulae, Z1 and Z2 represent an aromatic hydrocarbon ring, R1, R2a, R2b, R3a and R3b represent a substituent, k, p1 and p2 denotes an integer of 0 to 8, q denotes an integer of 0 to 4, m1, m2, n1 and n2 denotes an integer of not less than 0, A1a and A1b represents an alkylene group, and A2a, A2b and A3 represents a divalent hydrocarbon group.