Foamed Polymeric Bottle Cap With Unfoamed Skin Layers
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Solution Overview
Problem
The increasing costs of plastic materials used in manufacturing plastic caps for bottles, particularly due to the high cost of hydrocarbons, necessitate a reduction in material usage while maintaining the functional, physical, and chemical properties of the caps.
Innovation Solution
A cap design featuring a sealing portion with a foamed plastic core sandwiched between two unfoamed plastic layers, utilizing a formulation with a propylene-based polyolefin and a blowing agent, allowing for reduced material usage while maintaining mechanical stiffness and chemical resistance, and a manufacturing process that selectively foams specific regions of the cap during injection molding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the cap is made entirely of unfoamed plastic material to ensure mechanical stiffness and strength, then the structural integrity is maintained, but the amount of raw material used increases leading to higher costs
Solution Approach 1:
The cap is designed with a multilayer structure where different regions have different foam densities. The skin layers (first and third regions) are made of unfoamed or low-density foamed material to maintain strength and seal integrity, while the core layer (second region) uses medium-density foamed material to provide stiffness with reduced material quantity. This local differentiation allows each region to perform its specific function optimally while minimizing overall material usage.
Solution Approach 2:
The cap combines multiple materials with different foam densities in a single structure. The composite structure consists of unfoamed plastic material layers (providing strength and sealing) combined with foamed plastic material layers (providing stiffness with lower density). This composite approach allows the cap to achieve the required mechanical properties while reducing the total amount of raw material needed compared to a fully unfoamed design.
2Strength
If the cap thickness is increased to ensure sufficient stiffness, then the mechanical strength is improved, but the weight and material costs increase
Solution Approach 1:
The cap incorporates foamed plastic material with controlled porosity in the core region. The foam structure provides the necessary stiffness and structural support while having significantly lower density than solid unfoamed material. This allows the cap to maintain adequate thickness for stiffness requirements while substantially reducing the weight and material quantity compared to a fully solid construction.
Solution Approach 2:
Different regions of the cap have different material densities optimized for their specific functions. The skin layers use unfoamed or low-density material for strength and sealing, while the core uses medium-density foamed material for stiffness. This local optimization allows the cap to achieve required mechanical properties with minimal overall weight and material usage.
3Quantity of substance
If a multilayer foamed structure is implemented to reduce material usage, then the material costs are reduced, but the manufacturing process complexity increases
Solution Approach 1:
The blowing agent is pre-mixed into the plastic material formulation before injection molding. The masterbatch containing the blowing agent is prepared in advance and homogenized in the screw/barrel assembly. During injection molding, the material is thermally activated and foams in situ within the mold cavity, eliminating the need for post-molding foaming operations or complex multi-step manufacturing processes.
Solution Approach 2:
The mechanical foaming process is replaced by in-situ chemical foaming during injection molding. Instead of mechanically forming foam structures separately and assembling them, the blowing agent chemically generates gas bubbles within the molten plastic during injection, creating the foamed structure in a single integrated process step.
4Stability of the object's composition
If the blowing agent proportion is increased to achieve better foaming, then the foam density is improved, but the material formulation complexity and cost increase
Solution Approach 1:
A masterbatch serves as an intermediary carrier for the blowing agent. The blowing agent is pre-dispersed in a compatible resin matrix at controlled concentrations (0.3-2.5% by weight of active components). This masterbatch simplifies the formulation process by providing a ready-to-use, homogenized material that ensures consistent foaming performance without requiring complex blending operations or precise dosing of pure blowing agent.
Solution Approach 2:
The blowing agent concentration is optimized within a specific range (0.3-2.5% by weight of active components) to achieve the desired foam density and structure. This parameter optimization balances foaming performance with material cost and formulation simplicity, avoiding both insufficient foaming (too low concentration) and excessive foaming or formulation complexity (too high concentration).
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 cap design achieves a significant reduction in material costs by minimizing raw material usage while ensuring the cap's mechanical strength and sealing efficiency, capable of withstanding pressures like those from carbonated beverages.
Implementation Method 1
a formulation comprising at least one propylene-based polyolefin and at least one blowing agent
Implementation Method 2
The homogenization and thermal activation of the blowing agent take place in a screw/barrel assembly
Data Source
AI summary
A cap for a bottle, which comprises at least a sealing portion and a lateral portion for fastening to the bottle. The sealing portion comprises, along a direction substantially perpendicular to the lateral portion, a first region formed of unfoamed polymeric material, a second region formed of foamed polymeric material, and a third region formed of unfoamed polymeric material, the second region being positioned between the first region and the third region. The disclosure also relates to a process for manufacturing a cap made of foamed polymeric material.