Prepreg Viscosity Control via Surface Photopolymerization
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Solution Overview
Problem
Current methods for producing prepregs with high reinforcing fiber weights (250-2,000 g/m²) face challenges in achieving void-free impregnation, flexibility, and tack properties, leading to issues like springback and handling difficulties due to viscosity-related trade-offs.
Innovation Solution
A method involving a matrix resin composition with epoxy resin, radically polymerizable unsaturated compounds, and a polymerization initiator, where the polymerization initiator is selectively activated on the surface to increase viscosity only in the superficial part, preventing voids and enhancing flexibility and tack properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the temperature of drying for removing the solvent is too high, then the solvent is removed more efficiently, but the thermally curable resin cures at the prepreg stage and the working life is shortened
Solution Approach 1:
The patent uses a solvent that evaporates at low temperature to remove the solvent without triggering resin curing. The solvent is replaced with one having a lower boiling point and better compatibility with the thermally curable resin, allowing complete evaporation during prepreg production and storage without causing premature curing.
2Ease of manufacture
If the viscosity of the matrix resin is low, then the impregnation of reinforcing fiber assembly is easier, but the tack property of the prepreg surface is excessive and handling becomes difficult
Solution Approach 1:
The patent uses a thermally curable resin with low initial viscosity that increases upon heating. During impregnation, the low viscosity allows easy penetration into the fiber assembly. During molding, heating increases the viscosity to provide appropriate tack property for layer bonding and handling stability.
3Ease of operation
If the viscosity of the matrix resin is high, then the tack property and handling are improved, but the impregnation of reinforcing fiber assembly becomes difficult and voids are generated
Solution Approach 1:
The patent employs a thermally curable resin whose viscosity dynamically changes with temperature. The resin starts with low viscosity for easy impregnation, then viscosity increases upon heating during molding to provide tack property and handling stability. This dynamic viscosity adjustment resolves the contradiction between impregnation ease and handling ease.
4Productivity
If a thick reinforcing fiber assembly is used to obtain a thick prepreg, then the productivity of molding is improved, but the impregnation with matrix resin becomes difficult due to high viscosity and voids are generated
Solution Approach 1:
The patent uses a thermally curable resin with low initial viscosity that enables complete impregnation of thick fiber assemblies. Upon heating during molding, the resin viscosity increases to provide tack property for layer bonding and prevent void formation, allowing production of thick prepregs without compromising impregnation quality.
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 method ensures void-free impregnation, superior flexibility, and appropriate tack properties, enabling the production of prepregs suitable for large-sized structural materials without springback, improving handling and physical properties of the resulting fiber-reinforced composite materials.
Implementation Method 1
a polymerization initiator that generates radicals
Data Source
Figure 1~2
Figure 3~5
AI summary
The present invention relates to a method for producing a prepreg which contains reinforcing fibers and a matrix resin composition with the weight per square meter of the reinforcing fibers being 250-2,000 g / m2. The production method comprises the following steps (1)-(3): (1) a matrix resin composition blending step for obtaining a matrix resin composition by mixing an epoxy resin, a radically polymerizable unsaturated compound, an epoxy resin curing agent and a polymerization initiator that generates radicals, in said step the content of the radically polymerizable unsaturated compound relative to 100% by mass of the total of the epoxy resin and the radically polymerizable unsaturated compound being 10-25% by mass; (2) a matrix resin composition impregnating step; and (3) a surface viscosity increasing step.