HDPE/LDPE Polymer Blend for Stretch Blow Molding
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Solution Overview
Problem
Conventional stretch blow molding technologies face limitations with high impact polystyrene (HIPS) due to environmental stress crack resistance, low temperature toughness, and water vapor transmission rate, while high density polyethylene (HDPE) has a narrow processing window, making it impractical for commercial manufacturing.
Innovation Solution
A polymer blend comprising at least 70% HDPE and 10% low density polyethylene (LDPE) is used, which increases melt strength and widens the processing window, allowing for controlled thinning during stretching and processing in conventional stretch-blow forming equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If HIPS is used for compression blow forming, then the processing is suitable for the CBF process, but the environmental stress crack resistance, low temperature toughness, and water vapor transmission rate are insufficient
Solution Approach 1:
The patent uses a composite material system consisting of HDPE as the base polymer combined with specific additives (nucleating agents, processing aids, and modifiers) to create a material that maintains processability while improving environmental stress crack resistance, low temperature toughness, and water vapor transmission rate properties
2Reliability
If HDPE is used to substitute HIPS, then the environmental stress crack resistance, low temperature toughness, and water vapor transmission rate are improved, but the processing window becomes very narrow making it impractical for commercial manufacturing
Solution Approach 1:
The patent modifies processing parameters including temperature ranges, strain rates, and molding pressures to expand the effective processing window of HDPE, making it suitable for commercial stretch blow molding operations while maintaining the improved reliability properties
Solution Approach 2:
The patent introduces processing aids and modifiers as intermediary substances that facilitate the processing of HDPE by improving melt flow characteristics and reducing sensitivity to processing parameter variations, thereby widening the practical processing window
3Productivity
If thin wall thickness is used to increase packaging efficiency ratio, then the milliliters of contents per weight of container increases, but the mechanical properties and processing control become more difficult
Solution Approach 1:
The patent implements variable wall thickness distribution within the container structure, providing thicker walls in high-stress areas (such as the base and shoulder regions) while maintaining thin walls in less critical areas, thereby achieving both high packaging efficiency and adequate mechanical strength
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 HDPE/LDPE blend enables the production of thin-walled containers with improved mechanical properties and processing efficiency, overcoming the limitations of HIPS and HDPE's narrow processing window, while maintaining a wider temperature and strain rate range.
Implementation Method 1
The HDPE/LDPE blends used in the practice of this invention provide increased melt strength resulting in a wider processing window
Data Source
AI summary
Stretch blow molded articles, e.g., thin wall containers, are made from a polymer blend comprising at least 70 percent by weight HDPE and at least 10 percent by weight LDPE based upon the total weight of the polymer blend. The HDPE/LDPE blends used in the practice of this invention provide increased melt strength resulting in a wider processing window.