Hot Fill Closures Using High Density Polyethylene
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Solution Overview
Problem
Existing hot filling processes face challenges in finding materials that provide adequate heat resistance, sealing properties, and resistance to cracking and deformation for closures, especially due to the complex geometries and small dimensions of plastic closures, which are difficult to test using standard deformation measurement methods.
Innovation Solution
The use of high density polyethylene compositions with specific bimodal molecular weight distributions and short chain branch ratios, which are tested using a compressive strain model to ensure suitable deformation properties for hot fill and aseptic fill applications, providing closures with improved heat resistance and sealing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If standard deformation test methods (ASTM D-2990) are used to test closures, then testing can be performed using standard compression molded specimens, but the complex geometries and small dimensions of plastic closures cannot be properly represented
Solution Approach 1:
The patent creates a mathematical model that copies the deformation behavior of actual closures with complex geometries. Instead of physically testing standard specimens that don't represent real closures, the model reproduces the stress-strain relationships and deformation characteristics of actual closure components, allowing accurate prediction of closure performance under various loading conditions.
Solution Approach 2:
The patent transforms the testing approach by changing from physical specimen testing to computational parameter analysis. The model uses material properties, geometric parameters, and loading conditions as inputs to predict deformation behavior, allowing accurate assessment of closure performance without requiring physical prototypes or standard specimens.
2Reliability
If high density polyethylene compositions are used for closures in hot fill processes, then heat resistance and sealing properties are improved, but resistance to deformation under thermal stress may be compromised
Solution Approach 1:
The patent applies different material properties to different regions or aspects of the closure material. The high density polyethylene composition is selected to provide excellent sealing properties at the sealing surface while the overall material structure and cross-linking are designed to maintain dimensional stability and resistance to deformation in the bulk material during thermal cycling.
Solution Approach 2:
The patent uses cross-linked high density polyethylene, which can be considered a composite structure at the molecular level. The cross-linking creates a three-dimensional network that combines the sealing properties of HDPE with enhanced thermal stability and deformation resistance, effectively creating a material with superior combined properties.
3Reliability
If closures are subjected to hot fill processes with temperatures from 70 to 93°C, then sterilization of the closure interior is achieved, but deformation and cracking may occur
Solution Approach 1:
The patent employs a mathematical model to predict and cushion against potential deformation and cracking before they occur. By analyzing the stress-strain behavior and thermal properties of the closure material, the model identifies formulations and designs that will withstand the thermal stress of hot fill processing, preventing deformation and cracking before they can compromise the closure.
Solution Approach 2:
The patent converts the potentially harmful thermal stress from the hot fill process into a beneficial sterilization effect. The controlled thermal cycling at 70-93°C is designed to be sufficient for sterilization while remaining below the threshold for damaging deformation, effectively using the heat for its beneficial purpose while avoiding its harmful effects through proper material selection and process control.
Data Source
AI summary
High density (density ≥0.950 g/cm3) polyethylene compositions for use in hot fill closures and processes.