PET Container Base Forming via Movable Ring Inversion
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Solution Overview
Problem
Current methods for producing polyethylene terephthalate (PET) containers with high crystallinity face challenges in achieving the necessary biaxial molecular orientation and clarity, while also requiring significant force to form the base structure due to internal pressures.
Innovation Solution
A method involving a mold assembly with a movable ring insert that forms a thinned flex point in the base portion, allowing for biaxial orientation and reduced force requirement by inverting the central inset portion under vacuum forces post-cooling, enabling the production of PET containers with enhanced crystallinity and clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a base insert and ring insert are raised up into position against a heel insert to form the base structure, then the container base can be formed with proper structure, but significant force is required to overcome internal pressures
Solution Approach 1:
The patent inverts the traditional base forming approach by allowing the preform to be blown into a void space first, creating an annular projection, and then using a movable ring that advances into the void to retract the projection into the base portion. This reverse sequence reduces the force needed compared to pushing components against high internal pressure.
Solution Approach 2:
The preform is blown into the void space between the base insert and heel insert before the movable ring advances. This preliminary action creates the annular projection that will later be retracted, allowing the base structure to form in a sequence that minimizes force requirements.
2Stability of the object's composition
If thermal processing is applied to amorphous PET material, then crystal growth is promoted, but the resulting material becomes opaque due to spherulitic morphology
Solution Approach 1:
The patent applies mechanical processing (biaxial orientation) before thermal processing. The preform is stretched along the longitudinal axis and expanded along the transverse axis to create biaxial molecular orientation. This preliminary mechanical orientation ensures that subsequent thermal processing promotes crystal growth while maintaining clarity, because the oriented molecular structure prevents spherulitic morphology formation.
Solution Approach 2:
The patent controls the timing and temperature parameters of thermal processing. Heat setting is performed at approximately 250°F - 350°F (121°C - 177°C) for two to five seconds after mechanical orientation. By controlling these parameters and applying thermal processing only after biaxial orientation is achieved, the patent promotes crystal growth while maintaining container clarity.
3Manufacturing precision
If mechanical processing is applied to orient amorphous material, then biaxial orientation is achieved, but only approximately 20% crystallinity is produced which is insufficient for hot-fill applications
Solution Approach 1:
The patent combines mechanical processing and thermal processing in a sequential manner. Mechanical processing (stretching and expanding) is performed first to achieve biaxial orientation, then thermal processing (heat setting) is applied to promote additional crystal growth. This combination achieves the higher crystallinity (25%-35%) required for hot-fill applications while maintaining the biaxial orientation and clarity.
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 allows for the production of PET containers with improved crystallinity and clarity, reducing the force needed to form the base structure and enhancing the container's material integrity and light transmission properties.
Implementation Method 1
The preform is blown against the mold cavity to form a body defining a base portion
Implementation Method 2
The commodity is allowed to cool causing a vacuum in the container that results in a central inset portion defined at the thinned flex point to invert
Data Source
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AI summary
Accordingly, the present disclosure provides a container and method of making a container. In one example, a preform is disposed into a mold cavity having a base forming assembly. The base forming assembly includes a base insert and a movable ring insert. The preform is blown against the mold cavity to form a body defining a base portion. The movable ring insert is advanced into the base portion to form a thinned flex point in the base portion while keeping the base insert fixed. The container is hot-filled with a commodity. The commodity is allowed to cool causing a vacuum in the container that results in the upward movement or inversion of a central inset portion defined at the thinned flex point.