Prepreg Sizing Composition for Adhesion and Storage Stability
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Solution Overview
Problem
Conventional epoxy resin combinations fail to achieve both high adhesion between carbon fibers and a matrix resin and long-term storage stability in carbon fiber-reinforced composite materials, as they do not simultaneously satisfy the requirements of having an epoxy component with high adhesion on the inner side of the sizing layer, a surface layer that suppresses reactions between the matrix resin and the epoxy compound, and a chemical composition that strongly interacts with the matrix resin.
Innovation Solution
A prepreg comprising sizing agent-coated carbon fibers with a thermosetting resin composition that includes an aliphatic epoxy compound and an aromatic epoxy compound in a specific ratio, along with a thermosetting resin and a latent hardener, which provides excellent adhesion and stability by preventing reactions between the matrix resin and the epoxy compound during long-term storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If epoxy compounds with high reactivity are used to improve adhesion, then bond strength is improved, but long-term storage stability deteriorates due to premature reactions
Solution Approach 1:
The sizing agent uses local quality differentiation to control reactivity spatially: the inner layer contains aliphatic epoxy compounds with high reactivity for strong carbon fiber bonding, while the outer layer contains aromatic epoxy compounds with lower reactivity that prevent premature reactions during storage. This spatial separation of reactivity levels resolves the contradiction between bond strength and storage stability.
Solution Approach 2:
The sizing agent is applied to carbon fibers in advance with a controlled composition that prevents premature reactions during storage. The outer layer's aromatic epoxy compounds act as a protective barrier that suppresses premature crosslinking, allowing the prepreg to be stored for extended periods before composite fabrication, while still maintaining high bond strength potential.
2Ease of manufacture
If a single-type epoxy sizing agent is used to simplify composition, then manufacturing complexity is reduced, but adhesion performance deteriorates
Solution Approach 1:
The sizing agent employs a composite structure combining aromatic and aliphatic epoxy compounds in specific ratios and spatial distributions. This composite approach achieves superior adhesion performance by leveraging the complementary properties of both epoxy types, resolving the contradiction between composition simplicity and adhesion performance.
Solution Approach 2:
The invention optimizes specific parameters including the ratio of aromatic to aliphatic epoxy compounds (0.3 to 2.0 by weight), the thickness distribution of inner and outer layers, and the molecular weight ranges of each epoxy type. By precisely controlling these parameters, the sizing agent achieves high adhesion performance while maintaining manufacturability through defined compositional specifications.
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 solution achieves excellent adhesiveness between the matrix resin and carbon fibers, maintains mechanical characteristics over time, and ensures high strength and heat resistance in carbon fiber-reinforced composite materials.
Implementation Method 1
the sizing agent includes an aliphatic epoxy compound (A) and an aromatic compound (B) at least containing an aromatic epoxy compound (B1)... excellent adhesiveness between a matrix resin and carbon fibers
Implementation Method 2
a thermosetting resin composition impregnated into the sizing agent-coated carbon fibers... the thermosetting resin composition includes a thermosetting resin (D) and a latent hardener (E)
Data Source
AI summary
A prepreg includes; sizing agent-coated carbon fibers coated with a sizing agent; and a thermosetting resin composition impregnated into the sizing agent-coated carbon fibers. The sizing agent includes an aliphatic epoxy compound (A) and an aromatic compound (B) at least containing an aromatic epoxy compound (B1). The thermosetting resin composition includes a thermosetting resin (D) and a latent hardener (E), and optionally includes an additive (F) other than the thermosetting resin (D) and the latent hardener (E). The (a)/(b) ratio is within a predetermined range where (a) is the height of a component at a binding energy assigned to CHx, C—C, and C═C and (b) is the height of a component at a binding energy assigned to C—O in a C1s core spectrum of the surfaces of the sizing agent-coated carbon fibers analyzed by X-ray photoelectron spectroscopy.