Multilayer Foam Sheet Structure for Shear Strength and Flexibility
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Solution Overview
Problem
Conventional foam sheets used in electronic devices lack flexibility and mechanical strength in the shear direction, fail to conform to level differences, and have inadequate gas sealability and reworkability, leading to issues such as screen unevenness, insufficient waterproofness, and difficulty in maintaining gas-purged environments.
Innovation Solution
A multilayer foam sheet comprising a base layer and a surface layer, with specific properties including low-speed shear modulus, compressive strength, and moisture permeability, designed to enhance flexibility, mechanical strength, and gas sealability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the expansion ratio of a foam is lowered to improve mechanical strength in the shear direction, then the mechanical strength is improved, but the flexibility decreases
Solution Approach 1:
The foam sheet is divided into multiple layers with different expansion ratios. The first layer has a lower expansion ratio (1.1-3.0) to provide mechanical strength, while the second layer has a higher expansion ratio (3.1-20.0) to provide flexibility. This segmentation allows each layer to specialize in one function, resolving the contradiction between strength and flexibility.
Solution Approach 2:
Different regions of the foam sheet (different layers) are given different properties. The first layer near the adhesive side has low expansion for strength, while the second layer on the outer side has high expansion for flexibility. This local differentiation of properties allows the same sheet to simultaneously achieve both mechanical strength and flexibility.
2Reliability
If a conventional foam sheet is used for sealing, then it provides basic cushioning property, but it fails to conform to level differences in the housing
Solution Approach 1:
The foam sheet uses layers with different expansion ratios to change its physical parameters. The high expansion ratio of the second layer (3.1-20.0) provides greater compressibility and conformability to level differences, while the low expansion ratio of the first layer maintains sealing reliability. This parameter differentiation resolves the contradiction between reliable sealing and ease of conformability.
3Adaptability or versatility
If a foam sheet with high expansion ratio is used to improve flexibility, then the flexibility is improved, but the mechanical strength in the shear direction decreases
Solution Approach 1:
The foam sheet is segmented into layers with different expansion ratios. The first layer (lower expansion ratio of 1.1-3.0) provides mechanical strength, while the second layer (higher expansion ratio of 3.1-20.0) provides flexibility. This segmentation allows the sheet to simultaneously achieve both high flexibility and adequate mechanical strength.
Solution Approach 2:
The foam sheet is a composite structure combining materials with different expansion ratios in different layers. This composite approach allows the sheet to integrate the strength-providing characteristics of low expansion foam with the flexibility-providing characteristics of high expansion foam, resolving the contradiction between these two properties.
4Strength
If the gel fraction of the foam is increased to improve mechanical strength, then the mechanical strength is improved, but the reworkability decreases
Solution Approach 1:
The foam sheet applies local quality differentiation by controlling gel fraction in different layers. The first layer has a higher gel fraction (30-80%) for mechanical strength, while the second layer has a lower gel fraction (10-70%) for reworkability. This localized property distribution resolves the contradiction between strength and ease of repair.
Data Source
AI summary
Provided is a multilayer foam sheet excellent in flexibility and mechanical strength in the shear direction.A multilayer foam sheet of the present invention is a multilayer foam sheet including: a base layer including a foam layer, and a surface layer including a foam layer or a resin film and laminated on at least one side of the base layer directly or with another layer interposed therebetween, a low-speed shear modulus being 50 MPa or more, and a 25% compressive strength being 125 kPa or less.