PET Bottle Neck Oriented Crystallization for Hot Fill Stability
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Solution Overview
Problem
Biaxially stretched, blow molded PET bottles face challenges with neck deformation during hot filling, requiring thick walls for heat resistance, which increases material costs and reduces productivity due to limitations in mold face capacity and preform neck diameter.
Innovation Solution
The bottle neck is formed by expanding a test tube-like preform in the biaxial stretching and blow molding process, achieving a density of 1.368 g/cm3 through oriented crystallization and controlled mold temperature, allowing for a thin wall with high heat resistance without conventional thermal crystallization treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the preform neck has a large diameter to accommodate wide-mouthed bottle requirements, then the bottle can achieve wide mouth functionality, but productivity decreases due to mold face limitations
Solution Approach 1:
The patent divides the bottle into two distinct formation processes: the preform neck is formed by injection molding with a relatively large diameter to accommodate wide-mouthed bottle requirements, while the bottle body is formed by biaxial stretching and blow molding. This segmentation allows the neck to have sufficient diameter for wide mouth functionality while the mold face can still accommodate multiple preforms, thereby maintaining productivity.
2Adaptability or versatility
If the preform neck has a large diameter to enable wide-mouthed bottle production, then wide mouth functionality is achieved, but the number of preforms that can be molded in one shot decreases
Solution Approach 1:
The patent separates the neck formation (injection molding) from the body formation (blow molding), allowing the neck to have a larger diameter suitable for wide-mouthed bottles while the mold face can still accommodate multiple smaller preforms. This segmentation resolves the conflict between neck diameter requirements and mold face capacity.
3Reliability
If thermal crystallization treatment is applied to the neck to improve heat resistance, then heat-resisting property is enhanced, but the manufacturing process becomes more complex
Solution Approach 1:
The patent merges the thermal crystallization treatment into the blow molding process itself by controlling the mold temperature during forming. The mold temperature is maintained within a specific range (20°C to 100°C) to promote crystallization of the PET resin in the neck region during the blow molding operation, eliminating the need for separate post-processing thermal crystallization steps and reducing manufacturing complexity.
4Reliability
If a thick neck wall is used to prevent shrinkage and deformation during hot filling, then heat resistance and seal integrity are improved, but material cost increases
Solution Approach 1:
The patent changes the physical and chemical parameters of the resin material by controlling the mold temperature during blow molding to promote crystallization of the PET resin in the neck region. This crystallization increases the heat resistance and dimensional stability of the neck, allowing it to maintain seal integrity during hot filling without requiring an increased wall thickness, thereby reducing material consumption and cost.
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 approach enhances heat resistance and productivity by maintaining seal integrity and reducing material costs, enabling the production of wide-mouthed bottles with high thermal stability and efficient manufacturing processes.
Implementation Method 1
the neck of the bottle having the above-described feature also undergoes oriented crystallization through the stretching process step. Microcrystals are formed by this oriented crystallization and are used as the nuclei to further promote uniform and sufficient crystallization
Implementation Method 2
when the neck is in contact with the mold which has been heated to a predetermined mold temperature within a thermally crystallizable range for the PET series resin
Data Source
AI summary
A biaxially stretched, blow molded bottle made of a resin comprising at least one of polyethylene terephthalate and a copolymerized polyester comprising ethylene terephthalate. The bottle neck is formed, just as the bottle body is formed, by expanding a body of a preform in a shape of a test tube in a stretching step of the molding process. The bottle neck has an average thickness in a range of 0.6 to 1.8 mm, and at the bottle neck, the resin is partially crystallized and is in an oriented crystallized state. A ratio of an absolute value of crystallization enthalpy, ΔHc, to melting enthalpy, ΔHm (|ΔHc|/ΔHm) of the bottle neck is a value less than 0.1, and a rate of dimensional change in the outer diameter of the bottle neck is 0.2% or less.