Carbon Fiber Bundle Surface Structure for Stronger Resin Composites
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Solution Overview
Problem
Existing carbon fiber bundles face challenges in achieving high mechanical characteristics due to surface uneven structures and defects, leading to inadequate strength and elastic modulus, particularly in the surface layer, which affects the performance of fiber-reinforced resins used in applications like airplanes.
Innovation Solution
A carbon fiber bundle with specific surface characteristics, including a surface uneven structure of 0.6 µm or less in length, a difference in height of 5 to 25 nm, and an average roughness of 2 to 6 nm, along with a complete circular cross-section, enhanced strand strength, elastic modulus, and knot tenacity, and controlled surface energy and oxygen-containing functional groups, is developed to improve mechanical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a fiber bundle that is in a swollen state due to the presence of a solvent is drawn, then the solvent within a filament is rapidly squeezed out from the filament simultaneously upon drawing, but the resultant structure of the filament tends to be less dense and thus a desired filament that has a dense structure cannot be obtained
Solution Approach 1:
The patent applies preliminary action by conducting drawing in two distinct stages: first drawing the coagulated fiber before solvent removal, then drawing again after solvent removal. This preliminary sequencing of operations allows the fiber structure to be properly prepared and densified in the first drawing stage, preventing the rapid solvent extrusion problem that would occur in a single-stage drawing process.
Solution Approach 2:
The patent segments the drawing process into two separate drawing steps: a first drawing operation performed on the coagulated fiber, and a second drawing operation performed after solvent removal. This segmentation allows each drawing step to be optimized independently, with the first drawing establishing initial orientation and the second drawing achieving final density without rapid solvent extrusion.
2Strength
If dry-densification of a coagulated fiber that has a high-dense structure is performed, then excellent strength is developed, but a defective point is present near the surface layer
Solution Approach 1:
The patent applies preliminary action by performing the first drawing operation on the coagulated fiber before solvent removal, which prepares the fiber structure in advance. This preliminary structuring ensures that when subsequent processing occurs, the surface layer is already properly organized and less prone to defect formation, while still achieving high overall density and strength.
Solution Approach 2:
The patent applies local quality by creating different structural characteristics in different regions of the fiber. The surface layer is optimized for defect-free quality through controlled drawing conditions, while the interior is optimized for high density. This regional optimization allows the surface to maintain reliability while the bulk provides strength.
3Reliability
If a technique for suppressing the entry of an oil solution and a technique for suppressing defective point formation are both implemented, then the effect of stably suppressing the entry of an oil solution into the surface layer portion is insufficient and the effect of reinforcing a carbon fiber is still far from a sufficient level
Solution Approach 1:
The patent segments the manufacturing process into distinct stages with different objectives: coagulation, first drawing, solvent removal, and second drawing. This segmentation allows each stage to be optimized for its specific function without requiring complex additional steps for oil solution suppression and defect prevention, as these concerns are addressed inherently by the process sequencing.
Solution Approach 2:
The patent extracts the solvent from the fiber structure at a specific intermediate stage, before the final drawing operation. By removing the solvent at this point, the fiber achieves proper density and structural organization without requiring additional complex steps to prevent oil solution entry or defect formation, as the extracted solvent prevents these issues inherently.
Data Source
AI summary
Provided is a carbon fiber bundle for obtaining a fiber-reinforced resin having high mechanical characteristics. A carbon fiber bundle formed of single carbon fibers, each of which has no uneven surface structure of 0.6 µm or more in length extending in the longitudinal direction of the single fiber; which has an uneven structure having a difference in height (Rp-v) of 5 to 25 nm between the highest portion and the lowest portion of the surface of the single fiber and having an average roughness Ra of 2 to 6 nm; and which has a ratio of the major axis to the minor axis (major axis / minor axis) of a cross-section of the single fiber of 1.00 to 1.01, wherein a mass of the single fiber per unit length falls within the range of 0.030 to 0.042 mg/m; a strand strength is 5900 MPa or more; a strand elastic modulus measured by the ASTM method is 250 to 380 GPa; and a knot tenacity is 900 N/mm2 or more.