Multi-Layer OCA Sheet with Segmented Elastic Moduli

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Optically clear adhesive (OCA) sheets face challenges in maintaining adhesive strength and preventing air bubbles in high temperature and high humidity environments, especially when bonding substrates with different elasticities, leading to peeling issues and reduced visibility in display devices.

Innovation Solution

A multi-layer OCA sheet structure is developed, comprising a low storage elastic modulus intermediate adhesive layer and high storage elastic modulus surface-adhesive layers, with the intermediate layer containing polyurethane, to enhance flexibility and adhesiveness while preventing delay bubbles.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of stationary object

If a thick OCA sheet is used to eliminate air gaps and improve visibility, then the adhesive strength and bonding reliability deteriorate, causing peeling and delay bubbles in high temperature and humidity environments

Engineering Contradiction:

ImproveOCA sheet thicknessVSAvoidbonding reliability

Core Design Contradiction:

Length of stationary objectVSReliability

Solution Approach 1:

The OCA sheet is divided into multiple layers with different storage elastic moduli. The intermediate layer has a lower storage elastic modulus (1.0×10^4 to 15.0×10^4 Pa at 85°C) to provide flexibility and conformability, while the surface-adhesive layers have higher storage elastic moduli (3.0×10^4 to 30.0×10^4 Pa at 85°C) to ensure strong adhesion. This segmentation allows the sheet to maintain both thickness for eliminating air gaps and reliability for preventing peeling and bubbles.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the OCA sheet are assigned different mechanical properties. The intermediate layer is designed with lower rigidity to accommodate substrate unevenness and thermal expansion differences, while the surface-adhesive layers are designed with higher rigidity to ensure strong bonding to the substrates. This local differentiation of material properties resolves the contradiction between thickness and bonding reliability.

Inventive Principle:

Principle #3Local quality

2Reliability

If the storage elastic modulus of the OCA sheet is increased to prevent delay bubbles, then the flexibility and capability to conform to uneven surfaces deteriorate

Engineering Contradiction:

Improvedelay bubble preventionVSAvoidcapability to conform to uneven surfaces

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The OCA sheet is segmented into layers with different storage elastic moduli. The intermediate layer has lower storage elastic modulus to provide flexibility and conformability to uneven surfaces, while the surface-adhesive layers have higher storage elastic modulus to prevent delay bubbles. This segmentation allows each layer to perform its specific function, resolving the contradiction between bubble prevention and conformability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The OCA sheet uses a composite structure combining materials with different mechanical properties. The intermediate layer uses a material with lower storage elastic modulus for flexibility, while the surface-adhesive layers use materials with higher storage elastic modulus for rigidity and bubble prevention. This composite approach enables the sheet to simultaneously achieve both flexibility and delay bubble prevention.

Inventive Principle:

Principle #40Composite materials

3Ease of manufacture

If a single-layer OCA sheet structure is used to simplify manufacturing, then the adhesive strength and delay bubble prevention capability deteriorate in high temperature and humidity environments

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidadhesive strength

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The OCA sheet is segmented into multiple layers, each with specific functions. The intermediate layer provides flexibility and conformability, while the surface-adhesive layers provide strong adhesion and delay bubble prevention. This segmentation improves reliability without significantly complicating manufacturing, as each layer can be produced using standard processes and then laminated together.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs a composite multi-layer structure where each layer is made of specific materials with tailored properties. The intermediate layer uses a material with lower storage elastic modulus, while the surface-adhesive layers use materials with higher storage elastic moduli. This composite structure enhances adhesive strength and reliability while maintaining manufacturing feasibility through standardized production methods.

Inventive Principle:

Principle #40Composite materials

Data Source

PatentUS11267991B2Transparent adhesive optical sheet, laminate and bonded structure

Publication Date: 2022.03.08 BANDO CHEM IND LTD

AI summary

The present invention provides an optically clear adhesive sheet that has excellent flexibility and prevents delay bubbles in high temperature and high humidity environments. The optically clear adhesive sheet of the present invention sequentially includes a first surface-adhesive layer, an intermediate adhesive layer, and a second surface-adhesive layer. The first surface-adhesive layer and the second surface-adhesive layer each have a higher storage elastic modulus at 85° C. than the intermediate adhesive layer. The first surface-adhesive layer and the second surface-adhesive layer each have a storage elastic modulus at 85° C. of 3.0×104 Pa or higher and 30.0×104 Pa or lower. The intermediate adhesive layer has a storage elastic modulus at 85° C. of 1.0×104 Pa or higher and 15.0×104 Pa or lower. The intermediate adhesive layer contains polyurethane.