Polyimide Film Molecular Structure for Low Retardation

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Solution Overview

Problem

Polyimide films used in touch panels and flexible devices face issues with positioning accuracy, high Yellow Index (YI), high retardation (Rth), and poor toughness, which affect visibility and durability, and are challenging to manufacture due to low solubility in solvents.

Innovation Solution

A polyimide film with a specific molecular structure, including a bivalent organic group and a tetravalent organic group, optimized with structures that inhibit charge-transfer complexes and improve solubility, achieving low YI, low Rth, and high toughness, and enhanced manufacturing precision.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If polyimide film is used as substrate for flexible devices, then thermal oxidation resistance and heat resisting properties are improved, but positioning accuracy of elements and manufacturing precision deteriorate

Engineering Contradiction:

Improvethermal oxidation resistanceVSAvoidpositioning accuracy

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent modifies the chemical structure parameters of polyimide by introducing specific aromatic rings (sulfone groups, carbonyl groups) and controlling the ratio of aromatic rings to imide rings. This structural parameter change achieves both high heat resistance (Tg ≥ 250°C) and low retardation (Rth ≤ 100 nm), resolving the contradiction between thermal stability and manufacturing precision.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite polyimide structure combining multiple aromatic ring types (sulfone aromatic rings, carbonyl aromatic rings) with imide rings in specific ratios. This composite molecular structure achieves synergistic effects: the aromatic rings provide thermal stability while the controlled configuration reduces birefringence, enabling both heat resistance and positioning accuracy.

Inventive Principle:

Principle #40Composite materials

2Temperature

If polyimide film with high aromatic ring density is used to improve heat resistance, then thermal stability is improved, but solubility in solvent deteriorates

Engineering Contradiction:

Improveheat resistanceVSAvoidsolubility in solvent

Core Design Contradiction:

TemperatureVSEase of manufacture

Solution Approach 1:

The patent changes the chemical composition parameters by introducing sulfone groups and carbonyl groups into the aromatic rings, and controls the ratio of aromatic rings to imide rings within 0.5-2.0. These parameter changes maintain high Tg (≥250°C) while improving solubility through specific functional group interactions with solvents.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces polar functional groups (sulfone groups, carbonyl groups) at specific locations within the polyimide molecular structure. These local polar regions enhance solvent interaction and solubility without compromising the overall thermal stability provided by the aromatic ring framework.

Inventive Principle:

Principle #3Local quality

3Temperature

If conventional polyimide film is used, then thermal stability is maintained, but Yellow Index and retardation are high affecting visibility

Engineering Contradiction:

Improvethermal stabilityVSAvoidvisibility

Core Design Contradiction:

TemperatureVSIllumination intensity

Solution Approach 1:

The patent modifies the molecular structure parameters by introducing sulfone aromatic rings and carbonyl aromatic rings, and controls the aromatic ring to imide ring ratio. These changes simultaneously achieve high Tg (≥250°C), low Yellow Index (≤8), and low retardation (Rth ≤ 100 nm), resolving all three optical and thermal requirements.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite molecular structure combining sulfone aromatic rings, carbonyl aromatic rings, and imide rings in optimized ratios. This composite structure achieves synergistic optical properties: the aromatic rings provide thermal stability while their specific arrangement and ratios minimize charge-transfer complex formation, reducing yellowing and retardation for superior visibility.

Inventive Principle:

Principle #40Composite materials

4Stability of the object's composition

If polyimide film with high Rth is used in touch panel, then structural stability is maintained, but rainbow irregularity occurs and visibility deteriorates

Engineering Contradiction:

Improvestructural stabilityVSAvoidvisibility

Core Design Contradiction:

Stability of the object's compositionVSIllumination intensity

Solution Approach 1:

The patent changes the molecular configuration parameters by introducing sulfone groups and carbonyl groups into the aromatic rings, and controls the aromatic ring to imide ring ratio within 0.5-2.0. These parameter changes achieve structural stability (high Tg) while minimizing birefringence (low Rth), eliminating rainbow irregularity and improving visibility.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11078378B2Polyimide film, polyimide varnish, and product and layered product using the polyimide film

Publication Date: 2021.08.03 ASAHI KASEI KOGYO KABUSHIKI KAISHA

AI summary

To provide polyimide films that contain polyimide good in solubility in solvent and excel lent in workability and that are colorless, transparent and excellent in toughness, polyimide varnishes, and products and layered products using the polyimide film, the polyimide film is characterized by containing polyimide expressed by following general formula (1), and containing as A in the general formula (1), a structure expressed by following general formula (A-1), for example, structure expressed by following general formula (A-5).Herein, in the general formula (1), A represents a bivalent organic group, B represents a tetravalent organic group, and n is 2 or more.