Prepreg Impregnation Control for Void-Free Composite Laminates
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Solution Overview
Problem
Existing methods for producing fiber reinforced composite materials without autoclaves face challenges such as long molding times, high void formation, and poor handleability due to the difficulty in efficiently removing volatiles and trapped air, and the interlayer toughening technique with thermoplastic resin often results in incomplete impregnation and voids.
Innovation Solution
A prepreg with a degree of impregnation of 30 to 95% and a shift parameter of 0.10<σ<0.45, where the un-impregnated regions are shifted to the side with a thermoplastic resin, allowing efficient volatile removal and improved impact resistance without the need for autoclaves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If un-impregnated regions are made large to ensure continuity for efficient volatile removal, then void generation is reduced, but prepreg handleability deteriorates due to fiber fluffing and tearing
Solution Approach 1:
The patent applies local quality by creating asymmetric impregnation where the degree of impregnation varies across different regions of the prepreg. Specifically, the impregnation degree is controlled to be lower near the thermoplastic resin interface (creating continuous un-impregnated regions for volatile removal) and higher in other areas (maintaining fiber consolidation and handleability). This spatial variation in impregnation quality resolves the contradiction between void reduction and handleability.
Solution Approach 2:
The patent segments the impregnation process by controlling resin penetration to create distinct impregnated and un-impregnated regions within the fiber layer. The un-impregnated regions are specifically positioned and sized to form continuous pathways for volatile removal, while the impregnated regions maintain structural integrity. This segmentation allows simultaneous achievement of low void content and good handleability.
2Ease of manufacture
If molding is performed without autoclave using only vacuum pump and oven, then equipment cost is reduced, but molding time increases and voids remain
Solution Approach 1:
The patent applies preliminary action by pre-configuring the prepreg with un-impregnated regions and thermoplastic resin positioning before molding. This pre-arranged structure ensures that during vacuum molding, volatiles can be efficiently removed through the pre-formed un-impregnated pathways, and the thermoplastic resin automatically positions itself to seal voids. This eliminates the need for autoclave equipment while achieving short molding times and low void content.
Solution Approach 2:
The patent changes the physical parameters of the prepreg structure, specifically the degree of impregnation and the positioning of thermoplastic resin, to enable efficient volatile removal during vacuum molding. By controlling the impregnation degree to 30-95% and positioning un-impregnated regions adjacent to thermoplastic resin, the material parameters are optimized for rapid vacuum molding without autoclave, thereby reducing both equipment cost and molding time.
3Strength
If thermoplastic resin is used for interlayer toughening, then impact resistance is improved, but incomplete impregnation occurs leading to voids
Solution Approach 1:
The patent uses the un-impregnated regions as an intermediary mechanism between the thermoplastic resin and the fiber layers. These regions allow volatiles to escape during molding before the thermoplastic resin solidifies, preventing void formation. The thermoplastic resin then fills these same regions after volatile removal, ensuring complete impregnation and void-free structure while maintaining impact resistance benefits.
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 enables the production of fiber reinforced composite materials with reduced voids, enhanced impact resistance, and improved handleability, achieving efficient processing and mechanical properties in a short molding time.
Implementation Method 1
a thermoplastic resin [D] that is insoluble in the epoxy resin [B] and is localized at a surface on one side of the prepreg
Implementation Method 2
an epoxy resin composition containing an epoxy resin [B] and a hardener [C], the epoxy resin composition being partially impregnated into the reinforced fibers [A]
Data Source
AI summary
The objective of the present invention is to provide a prepreg and a fiber reinforced composite material using this prepreg. This prepreg has good handleability, is suitable for producing a reinforced composite material in a short-time and without using an autoclave, and is capable of yielding a fiber reinforced composite material exhibiting excellent impact resistance, wherein the occurrence of voids has been suppressed. To attain the objective, this prepreg comprises a reinforced fiber [A] that is layered and partially impregnated with an epoxy resin composition containing an epoxy resin [B] and a hardener [C], the impregnation rate φ being 30 to 95%. In this prepreg, a thermoplastic resin [D] insoluble in the epoxy resin [B] is distributed unevenly over a surface on one side of the prepreg, and a portion not impregnated with the epoxy resin composition is localized in the layer of the reinforced fiber [A] on the side where the thermoplastic resin [D] is distributed unevenly. This prepreg has a localization parameter σ, which defines the degree of the localization to be in the range of 0.10<σ<0.45.