PET Preform Wall Thickness and Crystallization for Heat Resistance
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Solution Overview
Problem
Large containers made of PET resin face challenges with heat resistance and transparency, particularly when subjected to hot water washing, leading to deformation and limited material usage due to blushing issues during stretch blow molding.
Innovation Solution
A preform for large containers is formed by injection molding with a wall thickness of 6 mm to 9 mm and a longer longitudinal axis length than the final product, followed by stretch blow molding, heat treatment, and final blow molding to enhance heat resistance and transparency, with specific temperature control to prevent blushing in the shoulder portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If PET resin is used for large containers to avoid EDC elution, then health safety is improved, but heat resistance deteriorates causing deformation during hot water washing
Solution Approach 1:
The patent applies parameter changes by controlling the crystallization temperature and degree of crystallinity of the PET resin. By annealing at specific temperatures (80-120°C) and controlling the crystallization process, the resin's thermal properties are modified to resist deformation during hot water washing while maintaining health safety.
Solution Approach 2:
The patent uses a composite structure combining PET resin with nucleating agents and crystallization promoters. This composite approach enhances the heat resistance of PET without compromising its inherent safety properties, allowing the container to withstand hot water washing temperatures.
2Strength
If the preform wall thickness is increased to enhance rigidity, then structural strength is improved, but blushing occurs during stretch blow molding reducing transparency
Solution Approach 1:
The patent optimizes the wall thickness parameter to a specific range (6-9 mm) that balances rigidity requirements with transparency preservation. Additionally, by controlling the crystallization parameters and using nucleating agents, the patent prevents blushing even at these optimized thicknesses, maintaining both strength and transparency.
Solution Approach 2:
The patent applies preliminary heat treatment and crystallization control during the preform manufacturing stage. By pre-annealing the preform at controlled temperatures and using crystallization promoters, the resin structure is prepared in advance to prevent blushing during subsequent stretch blow molding, thereby maintaining transparency while achieving required rigidity.
3Temperature
If the preform longitudinal axis length is increased to improve heat resistance, then thermal stability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent optimizes the preform longitudinal axis length parameter to achieve the necessary heat resistance while maintaining manufacturability. By carefully selecting this dimensional parameter and coordinating it with crystallization control, the patent achieves thermal stability without excessive manufacturing complexity.
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 method produces large containers with improved heat resistance and transparency, allowing for increased PET resin usage and rigidity, suitable for applications like refillable mineral water bottles without deformation or cracking from hot water washing.
Implementation Method 1
heat-treating the primary blow molded product to shrink it
Implementation Method 2
heat-treating the primary blow molded product to shrink it
Data Source
AI summary
A preform 20 for a large container, used for producing a large container which is made of a polyethylene terephthalate resin and which is formed by stretch blow molding, is formed by injecting molding to have a wall thickness of 6 mm to 9 mm and have a longitudinal axis length longer than that of the large container which is a final molded product.