Polypropylene Expanded Beads with Through Holes
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Solution Overview
Problem
Polypropylene-based resin expanded beads with high melting points face challenges in in-mold molding due to high vapor pressure requirements, leading to reduced voidage and limited pressure range for molding articles with excellent rigidity and high voidage.
Innovation Solution
The development of polypropylene-based resin expanded beads with through holes, featuring a foamed core layer and a cover layer, where the core layer comprises 70-97% of a polypropylene resin with a melting point between 140°C and 150°C, and 3-30% of a resin with a melting point between 145°C and 160°C, allowing for a specific crystal structure and melt flow rate that enables in-mold molding with low vapor pressure and high voidage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a polypropylene-based resin with a high melting point is used to obtain excellent rigidity, then the rigidity of the expanded beads molded article is improved, but the vapor pressure required for in-mold molding increases
Solution Approach 1:
The invention uses a composite resin composition containing two different polypropylene-based resins (PP1 with melting point 135-145°C and PP2 with melting point 145-155°C) in specific proportions. This composite approach allows the material to exhibit both low melting point characteristics (enabling low vapor pressure molding) and high rigidity (through the combined properties of the resin blend), thus resolving the contradiction between rigidity and vapor pressure requirements
Solution Approach 2:
The invention changes the melting point parameter of the resin composition by carefully selecting and blending two specific polypropylene-based resins with defined melting point ranges. This parameter optimization enables the resin to melt at lower temperatures during molding (reducing vapor pressure) while maintaining the rigidity required for the final product
2Strength
If a high vapor pressure is used in in-mold molding to achieve excellent rigidity, then the rigidity is improved, but the voidage of the molded article decreases
Solution Approach 1:
By optimizing the melting point parameter of the resin composition through selective blending of PP1 and PP2, the invention enables molding at lower temperatures and pressures. This parameter change prevents excessive compression of the expanded beads during molding, thereby maintaining high voidage while still achieving the required rigidity in the final product
3Strength
If a polypropylene-based resin with a high melting point is used to maintain rigidity, then the rigidity is improved, but the range of vapor pressure for in-mold molding is limited
Solution Approach 1:
The composite resin system combining PP1 and PP2 creates a material with optimized thermal properties that can be molded across a broader vapor pressure range. The synergistic effect of the two resins allows flexible molding conditions while maintaining product rigidity, thus expanding the adaptability of the molding process
Solution Approach 2:
The invention optimizes the melting point parameter of the resin composition to fall within a specific range (135-155°C) that enables versatile molding conditions. This parameter optimization allows the material to be processed under various vapor pressure conditions while consistently producing rigid products, thereby expanding the range of applicable vapor pressure values
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 solution allows for the production of expanded beads molded articles with excellent rigidity and high voidage across a wider pressure range, maintaining excellent mechanical properties and sound absorption while reducing the impact of high vapor pressure on voidage reduction.
Implementation Method 1
a polypropylene-based resin composition comprising 70 to 97% by weight of a polypropylene-based resin PP1 having a melting point of higher than 140°C and not higher than 150°C, and 3 to 30% by weight of a polypropylene-based resin PP2 having a melting point of not lower than 145°C and not higher than 160°C
Implementation Method 2
an expanded beads molded article with interconnected voids... having excellent water permeability, air permeability and sound absorbing property and also excels in cushioning property
Data Source
Figure 1~2(c)
Figure 2(d)~3(b)
Figure 3(c)~4
AI summary
An expanded bead having a through hole and including a foamed core layer which defines the through hole therein and which is constituted of a resin composition containing two kinds of polypropylene-based resins having different melting points, and a cover layer covering the foamed core layer and constituted of a polyolefin-based resin. The expanded bead gives a DSC curve in which an endothermic peak intrinsic to the resin composition and another endothermic peak on a higher temperature side thereof appear in a specific heat of fusion ratio.