Multilayered Sheet Thermoforming Thermal Stability
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Solution Overview
Problem
Current packaging sheets used for thermoforming and thermal processing are either difficult to thermoform or lack thermal stability, as they distort when exposed to high temperatures due to their composition, particularly those with polystyrene or polypropylene layers.
Innovation Solution
A multilayered sheet comprising a polyolefin layer with a high melting temperature and a polymer layer with a glass transition temperature above ambient, where the polyolefin's storage modulus is greater than the polymer's at 35°C, but crosses over at a midpoint temperature, providing both thermoformability and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a sheet comprises polystyrene for thermoforming, then thermoformability is improved, but thermal stability deteriorates as the sheet distorts at temperatures above 90°C
Solution Approach 1:
The patent employs a composite multilayer structure consisting of a polyolefin layer and a polymer layer with different thermal properties. The polyolefin layer provides thermoformability while the polymer layer with higher glass transition temperature provides thermal stability, allowing the composite sheet to maintain shape at temperatures above 90°C while still being thermoformable at lower temperatures.
Solution Approach 2:
The patent utilizes parameter changes by selecting materials with specific glass transition temperatures and melting points. The polyolefin has a glass transition temperature below ambient temperature for easy thermoforming, while the polymer layer has a glass transition temperature above ambient temperature to provide thermal stability at elevated temperatures, creating a temperature-dependent performance profile.
2Stability of the object's composition
If a sheet uses two exterior layers of polypropylene for thermal stability, then thermal stability is improved, but ease of manufacture deteriorates due to polypropylene's crystallinity and manufacturing limitations
Solution Approach 1:
Instead of using a homogeneous polypropylene structure that is difficult to manufacture, the patent creates a composite of polyolefin and polymer layers. This composite approach allows each layer to contribute its strengths while avoiding the manufacturing complexities of crystalline polypropylene, as the amorphous or semi-crystalline polyester layer can be more easily processed.
Solution Approach 2:
The patent applies local quality by assigning different functional roles to different layers. The polyolefin layer handles the thermoforming function while the polymer layer provides thermal stability, allowing each material to be optimized for its specific function rather than requiring the entire sheet to meet all requirements simultaneously, which simplifies manufacturing.
3Strength
If the polyolefin layer has high storage modulus at ambient temperature for rigidity, then structural strength is improved, but flexibility at processing temperature deteriorates
Solution Approach 1:
The patent exploits parameter changes with temperature by selecting a polyolefin with a glass transition temperature below ambient temperature. This ensures the material is rigid and structurally strong at room temperature but becomes flexible and easier to form when heated to processing temperatures, as the polymer chains gain mobility above the glass transition point.
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 sheet exhibits enhanced tear resistance, elongation, and compression strength, maintaining shape and stability up to 284°F (140°C), suitable for retort, aseptic, hot-fill, or microwave processing, with improved material distribution and oxygen barrier properties.
Implementation Method 1
a storage modulus (G′1) greater than about 100,000 psi (about 690 MPa) at ambient temperature
Implementation Method 2
a glass transition temperature greater than ambient temperature
Implementation Method 3
the ratio of G′1 to G′2 at about 35° C. is less than 1, and the ratio of G′1 to G′2 at the midpoint temperature is greater than one
Data Source
AI summary
A multilayered sheet is described. The sheet comprises a first layer comprising a polyolefin having a melting temperature, a storage modulus (G) greater than 100,000 psi (690 MPa) at ambient temperature, and a glass transition temperature less than ambient temperature; and a second layer comprising a polymer having a glass transition temperature greater than ambient temperature.