HDPE Formulation for Stretch Blow-Molding Bottles
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Solution Overview
Problem
The two-station stretch blow-molding process faces challenges with polypropylene and PET due to their low stiffness and poor recycling properties, and HDPE has not been effectively used in this process due to poor stretch compaction and non-uniform wall thickness issues.
Innovation Solution
A plastic formulation based on at least 60% HDPE with specific density and melt index ranges, optimized for both injection molding and stretch blow-molding, allowing for axial and radial stretching and enabling frictionless injection molding and sufficient stretch compaction, while maintaining comparable strength and recyclability to PET bottles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If HDPE is used as raw material in two-station stretch blow-molding process, then stiffness and recyclability are improved, but stretch compaction quality deteriorates due to poor stretch properties resulting in non-uniform wall thickness
Solution Approach 1:
The patent changes the molecular weight distribution parameters of HDPE by using a bimodal or multimodal blend with specific melt indices (first MI 0.1-0.9 g/10min at 190°C/2.16kg, second MI 5-50 g/10min at 190°C/21.6kg). This parameter modification enables the material to achieve both good stretch compaction for uniform wall thickness and sufficient stiffness for the final bottle structure.
Solution Approach 2:
The patent uses a composite HDPE formulation combining different HDPE grades with distinct molecular weight characteristics. The blend of high molecular weight HDPE (for stiffness and stretchability) and low molecular weight HDPE (for flow and compaction) creates a composite material that resolves the contradiction between structural requirements and manufacturing quality.
2Ease of manufacture
If conventional PET is used for plastic bottles, then processability in stretch blow-molding is improved, but recycling difficulty increases due to contamination with non-food-contact plastics
Solution Approach 1:
The patent modifies the material composition parameter by formulating HDPE with specific bimodal or multimodal molecular weight distribution and controlled melt indices. This enables HDPE to achieve processability comparable to PET in two-station stretch blow-molding while maintaining food-contact safety and recyclability, as HDPE can be easily separated in floating-sinking processes.
3Quantity of substance
If polypropylene is used for plastic bottles, then material availability is improved, but top load properties and creep resistance deteriorate due to low stiffness
Solution Approach 1:
The patent employs a composite HDPE formulation with bimodal or multimodal molecular weight distribution that combines the advantages of different HDPE grades. The resulting material achieves superior stiffness and top load properties compared to polypropylene, while maintaining good availability and processability.
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 formulation enables the production of strong, lightweight plastic bottles with reduced raw material use and lower petroleum consumption, facilitating easy recycling and minimizing CO2 release, while allowing for the use of existing PET processing tools and molds.
Implementation Method 1
In the stretch blow-molding process the preform is brought to the specified temperature for example by infrared radiation
Data Source
AI summary
An exemplary plastic formulation is disclosed for the production of plastic bottles in a two-stage stretch blow-molding process, and includes at least 60% of HDPE (High Density Polyethylene) having a density of 0.941 g/cm3 to 0.965 g/cm3 and according to ISO 1133 a melt index 190° C./2.16 kg of 0.1 to 0.9 g/10 min. The HDPE contains a mono-modal or multi-modal HDPE having a second melt index 190° C./21.6 kg of 5 g/10 min to 50 g/10 min according to ISO 1133. A method is disclosed for producing a plastic bottle in a two-stage stretch blow-molding process using the plastic formulation.