Prepreg Sheet Thickness Expansion Control
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Solution Overview
Problem
Conventional prepreg sheets made from carbon fibers and thermoplastic resin fibers tend to expand significantly in the thickness direction when heated, making it difficult to insert them into a mold and resulting in undesirable molded articles due to weak tangle forces and poor entanglement of fibers.
Innovation Solution
A prepreg sheet with a thickness expansion rate of 250% or less after heat treatment, featuring a density of needle punching marks of 3 punches/cm² or less, a basis weight of 100 to 1500 g/m², and a thickness of 0.5 to 6.0 mm, with carbon fibers and thermoplastic resin fibers mixed in a mass ratio of 20:80 to 80:20, and average fiber lengths of 15 to 100 mm, which controls expansion by suppressing the entanglement of carbon fibers with thermoplastic resin fibers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If carbon fibers and thermoplastic resin fibers are entangled by needle punching to form nonwoven fabrics, then the fibers are blended and sheeted, but the thermoplastic resin fibers melt and spread when heated, causing the prepreg sheet to expand in the thickness direction
Solution Approach 1:
The patent applies preliminary anti-action by using a specific needle punching density (3 punches/cm² or less) to create initial entanglement that counteracts the subsequent spreading tendency of thermoplastic resin fibers when heated. This pre-established structure prevents the harmful expansion that would otherwise occur during heating and molding processes.
Solution Approach 2:
The patent changes the parameter of needle punching density to a specific value (3 punches/cm² or less) to achieve the optimal balance between fiber entanglement and prevention of thickness expansion. This parameter optimization ensures that the prepreg sheet maintains dimensional stability during heating while still achieving adequate fiber bonding.
2Strength
If the density of needle punching marks is increased to enhance fiber entanglement, then the nonwoven fabric structure is strengthened, but the thickness expansion rate increases making it difficult to insert into molds
Solution Approach 1:
The patent uses preliminary anti-action by establishing a specific needle punching density (3 punches/cm² or less) that creates sufficient fiber entanglement to maintain structural integrity while simultaneously preventing the thickness expansion that would hinder mold insertion. This pre-configured structure counteracts both weaknesses identified in conventional methods.
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 prepreg sheet can be smoothly inserted into a mold and produces desirable molded articles by controlling thickness expansion, enhancing mechanical strength and homogeneity through optimized fiber lengths and ratios, and maintaining shape during heat and pressure treatment.
Implementation Method 1
When the nonwoven fabrics are heated and pressed to obtain molded articles, the thermoplastic resin fibers in the nonwoven fabrics melt and tend to spread.
Implementation Method 2
a prepreg sheet obtained by heating and pressing the nonwoven fabrics is tend to expand in the thickness direction because of the force of the carbon fibers to return to their original place before spreading
Data Source
Figure 1
Figure 2
Figure 3(a)~3(b)
AI summary
The prepreg sheet, which is an intermediate of molded articles, has a nonwoven fabric having carbon fibers and thermoplastic resin fibers, wherein the prepreg sheet has a thickness expansion rate of 250 % or less after being heated for 90 seconds at a temperature of the melting point of the thermoplastic resin fiber to the melting point + 100°C.