Low Density Microspheres for Resin-Free Sandwich Panels
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Solution Overview
Problem
Existing methods for fabricating sandwich panels with low-density structures face challenges such as increased weight due to resin usage and non-uniform density, which limits their application in various industries.
Innovation Solution
The development of a method to fabricate low-density polymeric microspheres with uniform density and size, specifically thermoplastic expandable microspheres, which are used to create a foam core for sandwich panels, eliminating the need for resin and achieving a uniform density below 15 kg/m3, and incorporating conductive additives for enhanced properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If resin is used to fill stitch holes in sandwich panels, then bonding between skins and core is improved, but weight increases
Solution Approach 1:
The invention extracts and eliminates the resin filling step from the traditional sandwich panel manufacturing process. Instead of using resin to fill stitch holes, the patent uses low-density microspheres that are distributed throughout the core material, eliminating the need for additional resin while maintaining bonding integrity through the mechanical interlocking of stitches and core material.
Solution Approach 2:
The invention discards the conventional approach of using resin fillers and recovers weight by using air-filled or low-density microspheres instead. This eliminates harmful resin material while recovering valuable weight reduction, achieving both debonding prevention and weight reduction goals.
2Strength
If traditional foam cores are used in sandwich panels, then structural support is provided, but density is non-uniform leading to unpredictable failure
Solution Approach 1:
The invention segments the continuous foam core into discrete, uniformly distributed low-density microspheres. Each microsphere acts as an independent structural unit with controlled density and size, eliminating the non-uniform density problems of traditional foam while maintaining structural support through the collective arrangement of these standardized units.
Solution Approach 2:
The invention changes the density parameter from continuous variation in traditional foam to discrete, controlled values in uniform microspheres. By controlling microsphere size, wall thickness, and material composition, the patent achieves predictable density values (e.g., 10-50 kg/m³) that ensure uniform structural performance and predictable failure modes.
3Strength
If high-density core materials are used, then mechanical strength is improved, but weight reduction goals are compromised
Solution Approach 1:
The invention creates a composite material system combining high-strength shell material (e.g., polyvinyl chloride, polyethylene) with air-filled interior space in microsphere structures. This composite approach achieves high specific strength (strength-to-weight ratio) by concentrating material where structurally necessary (in the shells) while minimizing weight through air-filled centers, enabling weight reduction while maintaining mechanical strength.
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
This approach results in lightweight sandwich panels with improved mechanical performance and reduced weight, enabling their use in applications like aerospace and impact resistance without the need for resin, while also providing conductive properties for electromagnetic interference shielding.
Implementation Method 1
The expandable microspheres are used as a blowing agent in products like, e.g., puff ink automotive underbody coatings or injection molding of thermoplastics. Typically, the product must be heated at some point in the process for the expandable microspheres to expand.
Implementation Method 2
incorporating conductive additives for enhanced properties
Data Source
AI summary
Low-density thermoplastic expandable microspheres are disclosed. Various low-density structures, in particular, sandwich panels, based on foam prepared from the low-density microspheres, are also disclosed. Process of preparing low-density polymeric microspheres, per se, and the corresponding low-density structures, based on the microsphere foam, are also disclosed.