Multilayer Foam Sheet Structure for Stress Relief and Peel Strength

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Solution Overview

Problem

Conventional foam sheets used in electronic devices face a trade-off between stress relaxation characteristics and tensile strength, leading to issues like image unevenness and poor reworkability, especially with the upsizing of displays.

Innovation Solution

A multilayer foam sheet comprising a base material layer and a surface layer, with specific stress relaxation rates and tensile strengths, ensuring flexibility and reworkability without causing image unevenness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a foam sheet with high stress relaxation characteristic is used, then image unevenness is prevented, but tensile strength becomes small causing breakage during peeling

Engineering Contradiction:

Improvestress relaxation characteristicVSAvoidtensile strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The foam sheet is divided into multiple layers (first foam layer, second foam layer, and resin film layer) where each layer contributes differently to the overall properties. The first foam layer provides stress relaxation, the second foam layer provides tensile strength, and the resin film layer enhances adhesion and strength, thus resolving the contradiction between stress relaxation and tensile strength through functional segmentation of layers

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite structure combining different foam materials and a resin film. The first foam layer and second foam layer have different densities and properties, combined with a resin film layer to create a composite material that simultaneously achieves high stress relaxation characteristic and high tensile strength, preventing both image unevenness and breakage during peeling

Inventive Principle:

Principle #40Composite materials

2Adaptability or versatility

If display size is increased, then viewing angle is improved, but strain from case is more easily transmitted to liquid crystal panel causing image unevenness

Engineering Contradiction:

Improvedisplay sizeVSAvoidstrain transmission

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The foam sheet is placed between the case and the liquid crystal panel to provide pre-cushioning against strain. The foam's compressibility and stress relaxation properties allow it to absorb and dissipate strain forces before they can reach the liquid crystal panel, preventing image unevenness even in large displays where strain transmission is more problematic

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 multilayer foam sheet effectively disperses stress, preventing image unevenness and ensuring easy peeling without breakage during rework.

Implementation Method 1

the multilayer foam sheet having a stress relaxation rate of 25% or more

Methodology Applied

Scientific EffectStress relaxation: Stress Relaxation

Data Source

PatentEP4691757A1Foam sheet and pressure-sensitive adhesive tape

Publication Date: 2026.02.11 SEKISUI CHEMICAL CO LTD

Figure 1

AI summary

A multilayer foam sheet including: a base material layer including a foam layer; and a resin layer including a foam layer or a non-foam layer on at least one side of the base material directly or via another layer; wherein the multilayer foam sheet has a stress relaxation rate of 25% or more; and the multilayer foam sheet has a tensile strength of 1.6 MPa or more.