Shear-Dependent Resin Backing for Composite Unrolling
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Solution Overview
Problem
The use of removable backing sheets in composite materials like prepregs and semipregs is wasteful and can lead to adhesion issues during unrolling, especially in automated processes, resulting in rejected materials, and attempts to increase resin viscosity to prevent adhesion reduce tack and drapability, limiting storage time.
Innovation Solution
A curable sheet-like composite material with a shear-dependent rheology outer backing layer that remains non-flowing during storage but exhibits viscous flow upon unrolling, allowing adjacent layers to separate without adhesion, eliminating the need for a removable backing sheet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a removable backing sheet is used to prevent adhesion during rolling, then the composite material can be stored in roll form, but the backing sheet is discarded as waste and adds to production cost
Solution Approach 1:
The invention extracts the backing sheet from the system by using the resin layer itself to provide the non-stick function. The resin layer is applied to the outer face of the composite material and provides a non-stick surface that prevents adhesion between adjacent layers during rolling, eliminating the need for a separate removable backing sheet.
Solution Approach 2:
The resin layer performs multiple functions: it provides the curable composite material properties and simultaneously serves as a non-stick backing layer during storage and handling. This multi-functionality eliminates the need for a separate backing sheet, reducing waste and production costs.
2Reliability
If resin viscosity is increased to prevent migration and blocking, then blocking is reduced, but the tack and drapability of the semipreg are reduced
Solution Approach 1:
The invention applies different properties to different parts of the system. The resin layer has high viscosity to prevent migration and blocking, while the inner composite material maintains appropriate viscosity for tack and drapability. This local differentiation allows each region to have the properties needed for its specific function.
Solution Approach 2:
The invention changes the viscosity parameter of the resin layer to be higher than the inner composite material, specifically controlling it to be in the range of 10-1000 Pa·s at 25°C. This parameter change prevents migration and blocking while the inner material maintains its processing properties.
3Duration of action of stationary object
If resin viscosity is increased to prevent migration, then blocking is prolonged, but storage time is still limited and tack is reduced
Solution Approach 1:
The invention optimizes the viscosity parameter of the resin layer to be in the range of 10-1000 Pa·s at 25°C, which provides long-term blocking prevention without significantly impacting storage time. This parameter range allows the resin to remain stable during storage while maintaining adequate processing properties.
Solution Approach 2:
The resin layer acts as an intermediary between the inner composite material and the external environment. It prevents migration and blocking by providing a stable, high-viscosity barrier layer that protects the inner material during storage and handling.
4Productivity
If a backing sheet is applied in automated process, then production efficiency is improved, but adhesion issues during unrolling may cause entire stack to be rejected
Solution Approach 1:
The invention removes the separate backing sheet component from the system, using instead a resin layer with controlled viscosity (10-1000 Pa·s at 25°C) that provides non-stick properties. This resin layer is applied in the automated process along with the inner composite material, maintaining production efficiency while ensuring reliable unrolling without adhesion issues.
Data Source
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AI summary
A curable sheet-like composite material comprising curable resin and at least one layer of structural fibres, and comprising an outer backing layer having a shear- dependent rheology, whereby the backing layer exhibits essentially no flow at rest on the outer surface of the composite material and exhibits a viscous flow response to induced shear.