Carbon Fiber Surface Roughness for Resin Impregnation
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Solution Overview
Problem
Carbon fiber reinforced polymer (CFRP) tanks for hydrogen gas tanks face challenges in achieving high strength due to voids and uneven resin content, which are exacerbated by the circularity and surface roughness of carbon fiber monofilaments, leading to insufficient resin impregnation and variations in fiber volume content.
Innovation Solution
The production of carbon fibers with controlled surface center line average roughness (Ra) between 6.0 nm and 13 nm and a long diameter/short diameter ratio of 1.11 to 1.245, along with specific processing methods such as coagulation, drawing, and stabilization, to enhance the bundling and impregnation properties of the carbon fiber bundles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the circularity of the cross-sectional shape of monofilaments is increased, then the gaps between monofilaments decrease and bundling property improves, but resin impregnation becomes insufficient leading to voids in CFRP
Solution Approach 1:
The patent intentionally introduces asymmetric surface features (wrinkles) on otherwise circular monofilament cross-sections. The monofilaments maintain high circularity (0.97-1.03) but incorporate surface irregularities with specific amplitude (0.5-5.0 μm) and wavelength (10-100 μm) parameters. This asymmetric surface modification allows the monofilaments to maintain good bundling while creating adequate resin flow paths and impregnation channels, resolving the contradiction between bundling property and resin impregnation uniformity.
2Stability of the object's composition
If the depth of wrinkles on monofilament surfaces is decreased, then bundling property improves, but resin impregnation becomes insufficient leading to voids
Solution Approach 1:
The patent precisely controls the wrinkle parameters within specific ranges: amplitude of 0.5-5.0 μm and wavelength of 10-100 μm. These parameter changes optimize the balance between bundling property and resin impregnation. The controlled wrinkle depth ensures sufficient resin penetration while maintaining adequate monofilament contact for bundling, thereby improving CFRP strength without sacrificing structural integrity.
3Strength
If the circularity of monofilament cross-section is increased, then stress concentration is reduced, but resin impregnation becomes insufficient
Solution Approach 1:
The patent applies local quality modification by maintaining high circularity (0.97-1.03) for the overall monofilament cross-section to ensure good fracture toughness, while introducing localized surface wrinkles with specific amplitude (0.5-5.0 μm) and wavelength (10-100 μm) parameters. This local modification creates resin flow paths at the surface level without compromising the overall circular geometry, thereby maintaining both fracture toughness and resin impregnation uniformity.
4Manufacturing precision
If wrinkles on monofilament surfaces are made excessively deep, then resin impregnation improves, but bundling property deteriorates leading to non-constant impregnation
Solution Approach 1:
The patent precisely limits the wrinkle amplitude to 0.5-5.0 μm and wavelength to 10-100 μm to optimize the balance between resin impregnation and bundling property. These controlled parameter changes ensure that wrinkles provide sufficient resin flow paths while maintaining adequate monofilament contact for consistent bundling, thereby achieving both good impregnation and stable bundling properties.
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 reduces voids and unevenness in the CFRP tank, resulting in improved strength and uniformity of the carbon fiber bundle impregnation, thereby enhancing the mechanical properties of the CFRP tank.
Implementation Method 1
discharging an acrylonitrile-based polymer solution into a coagulation liquid to coagulate the polymer solution
Implementation Method 2
drawing the yarn at a draw ratio of 3.0 or more and 4.5 or less in a pressurized steam atmosphere at 130°C or higher and 160°C or lower
Implementation Method 3
a stabilization step of heating a carbon fiber precursor acrylic fiber bundle in an oxidizing atmosphere at 200°C or higher and 300°C or lower
Implementation Method 4
a pre-carbonization step of heating the stabilized fiber bundle at 550°C or higher and 800°C or lower in a non-oxidizing atmosphere to obtain a pre-carbonized fiber bundle
Data Source
AI summary
A first aspect of the present invention is carbon fiber wherein the surface of a monofilament has a center line average roughness Ra of 6.0 nm or more and 13 nm or less, and the monofilament has a long diameter/short diameter ratio of 1.11 or more and 1.245 or less. A second aspect of the present invention is carbon fiber precursor acrylic fiber wherein the surface of a monofilament has a center line average roughness Ra of 18 nm or more and 27 nm or less, and the monofilament has a long diameter/short diameter ratio of 1.11 or more and 1.245 or less. The carbon fiber according to the first aspect is obtained by stabilizing and carbonizing under specific conditions the carbon fiber precursor acrylic fiber according to the second aspect.