PLA Foamed Particles: Rotary Blade Cutting for Uniform Fusion
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Solution Overview
Problem
Existing methods for producing polylactic acid-based resin foam-molded articles face challenges in achieving both high heat resistance and mechanical strength due to low crystallinity and poor fusion bonding properties, primarily attributed to the molar ratio of optical isomers and the foaming process used in in-mold foam-molding.
Innovation Solution
The method involves extruding a polylactic acid-based resin with a molar ratio of D-form and L-form optical isomers where one isomer is less than 5 mol%, followed by cutting the extrudate with a rotary blade and cooling it to prevent cell section exposure, resulting in foamed particles with a skin layer and improved thermal fusion bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polylactic acid-based resin with high content of less optical isomer (≥5 mol%) is used to improve ease of manufacture, then the resin becomes easier to produce, but the crystallinity decreases and heat resistance deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the molar ratio of optical isomers (D-form and L-form) within 40/60 to 60/40 range, and controlling crystallinity between 30-80%. This optimization of compositional parameters enables the resin to achieve both manufacturability and sufficient heat resistance for practical applications.
2Temperature
If a highly crystalline polylactic acid-based resin (≤5 mol% less optical isomer) is used to improve heat resistance, then the heat resistance improves, but the fusion bonding property deteriorates during foaming
Solution Approach 1:
The patent optimizes the crystallinity parameter to fall within 30-80%, avoiding excessive crystallinity that would harm fusion bonding. This parameter optimization allows the resin to maintain both heat resistance and adequate fusion bonding properties during the foaming process.
Solution Approach 2:
The patent introduces a preliminary foaming step before the final foaming process. This preliminary action partially expands the particles, creating a structure that facilitates better fusion bonding during subsequent foaming, thereby resolving the contradiction between heat resistance and bonding properties.
3Ease of manufacture
If the polylactic acid-based resin is preliminarily foamed by heating to produce preliminarily foamed particles, then the foaming process is facilitated, but crystallization proceeds and mechanical strength decreases
Solution Approach 1:
The patent employs a two-stage foaming process where preliminary foaming is performed at controlled conditions followed by final foaming. This preliminary action creates a precursor structure that enables easier final foaming while controlling crystallization to preserve mechanical strength.
Solution Approach 2:
The foaming process is divided into periodic stages: preliminary foaming under controlled conditions, then final foaming at different parameters. This periodic action allows crystallization to occur in a controlled manner during preliminary foaming, while the final foaming stage completes the expansion without excessive crystallization, maintaining mechanical strength.
4Productivity
If particles are impregnated with foaming agent and foaming aid before preliminarily foaming, then the foaming efficiency is improved, but the process complexity increases
Solution Approach 1:
The patent combines the foaming agent and foaming aid into a single impregnation step, merging multiple functions into one operation. This integration improves foaming efficiency while minimizing the increase in process complexity by consolidating the treatment steps.
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 yields polylactic acid-based resin foamed particles with enhanced heat resistance, mechanical strength, and uniform foaming, leading to high-quality foam-molded articles with excellent appearance and thermal properties.
Implementation Method 1
cutting the extrudate with a rotary blade
Implementation Method 2
cooling it to prevent cell section exposure
Implementation Method 3
crystallization of the polylactic acid-based resin proceeds due to the heat added during the preliminary foaming process
Implementation Method 4
the foamed particles are fusion-bonded to unite together by the foam pressure of the polylactic acid-based resin foamed particles
Data Source
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AI summary
The present invention provides a method for producing polylactic acid-based resin foamed particles for in-mold foam-molding from which a polylactic acid-based resin foam-molded article excellent in heat resistance and mechanical strength can be obtained by in-mold foam-molding. In the method of the present invention for producing polylactic acid-based resin foamed particles for in-mold foam-molding, a rotary blade is rotated at a given rotation speed while being always in contact with the front end surface of a nozzle and a polylactic acid-based resin extrudate extrusion-foamed through a nozzle is cut with the rotary blade, so that it is possible to cut the polylactic acid-based resin extrudate surely to obtain substantially spherical polylactic acid-based resin foamed particles. Therefore, when polylactic acid-based resin foamed particles are used for in-mold foam-molding, the polylactic acid-based resin foamed particles foam uniformly in all directions and, as a result, the foamed particles are thermal fusin bonded to unite together strongly in all direction.