Polyurethane Optical Film Suppressing Rainbow Phenomenon

Solution Overview

Problem

Optical films with biaxially stretched polyester bases suffer from a rainbow phenomenon due to refractive index differences between the base film and intermediate coating layers, leading to reduced visibility and adhesion issues under high temperature and humidity conditions.

Innovation Solution

A polyurethane coating layer with a refractive index of 1.54 to 1.59, incorporating 0.5 to 30 wt% high refractive filler (refractive index of 2.0 or more) and an aromatic isocyanate compound, is applied to match the refractive index of the base film, enhancing adhesion and reducing the rainbow phenomenon.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an intermediate coating layer is added to improve adhesion between the base film and hard coating layer, then adhesion is improved, but a rainbow phenomenon occurs due to refractive index difference

Engineering Contradiction:

ImproveadhesionVSAvoidrainbow phenomenon

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The refractive index of the intermediate coating layer is adjusted by changing the chemical composition parameters. Specifically, a polyurethane resin with refractive index of 1.54-1.59 is selected, and high refractive filler (refractive index ≥2.0) is added at 0.5-30 wt% to tune the overall refractive index to match the base film (1.63-1.67), thereby eliminating the rainbow phenomenon while preserving adhesion improvement

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The intermediate coating layer is formulated as a composite material combining polyurethane resin (for adhesion properties) with high refractive filler particles (for refractive index matching). This composite structure allows simultaneous achievement of both adhesion enhancement and optical clarity by leveraging the complementary properties of the constituent materials

Inventive Principle:

Principle #40Composite materials

2Object-affected harmful factors

If high refractive filler is added to match the refractive index, then the rainbow phenomenon is suppressed, but manufacturing complexity and cost increase

Engineering Contradiction:

Improverainbow phenomenonVSAvoidmanufacturing complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The high refractive filler is selectively added only to the intermediate coating layer where refractive index matching is critical, rather than throughout the entire optical film structure. This localized application minimizes manufacturing complexity by focusing the complexity only where optically necessary

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The refractive index of the intermediate layer is precisely controlled within a specific range (1.54-1.59 for the resin component) to achieve optimal matching with the base film. This parameter optimization allows suppression of the rainbow phenomenon while maintaining manufacturability through standardized material specifications

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If the refractive index of the coating layer is reduced to match the base film, then the rainbow phenomenon is suppressed, but adhesion performance deteriorates

Engineering Contradiction:

Improverainbow phenomenonVSAvoidadhesion

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The intermediate coating layer is formulated as a composite material combining polyurethane resin (for adhesion properties) with high refractive filler particles (for refractive index matching). This composite structure allows simultaneous achievement of both adhesion enhancement and optical clarity by leveraging the complementary properties of the constituent materials

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The refractive index of the intermediate coating layer is adjusted by changing the chemical composition parameters. Specifically, a polyurethane resin with refractive index of 1.54-1.59 is selected, and high refractive filler (refractive index ≥2.0) is added at 0.5-30 wt% to tune the overall refractive index to match the base film (1.63-1.67), thereby eliminating the rainbow phenomenon while preserving adhesion improvement

Inventive Principle:

Principle #35Parameter changes

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 solution effectively suppresses the rainbow phenomenon and improves adhesion between the base film and hard coating layer, maintaining optical clarity and durability under varying environmental conditions.

Implementation Method 1

high refractive filler (refractive index of 2.0 or more) is included in a polyurethane coating layer of a refractive index of 1.54 to 1.59... the refractive index of the polyurethane coating layer is similar to the refractive index of the base film, which results in the improvement of the rainbow phenomenon

Methodology Applied

Scientific EffectRefraction: Refraction

Data Source

PatentUS8980385B2Optical film

Publication Date: 2015.03.17 MICROWORKS CO LTD

AI summary

Provided is an optical film including a polyurethane coating layer including high refractive inorganic materials to lower reflectivity without causing a rainbow phenomenon.