Polyethylene Shrink Films with Cyclic Olefin Copolymer
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Solution Overview
Problem
Current polyethylene films, particularly shrink films, face challenges in achieving sufficient transverse direction (TD) shrinkage while maintaining mechanical and optical properties, which limits their performance and efficiency in applications such as packaging.
Innovation Solution
Incorporating a cyclic-olefin copolymer (COC) into the polymer composition, with specific weight percentages and glass transition temperatures, to enhance TD shrinkage, stiffness, and optical properties, allowing for improved load retention resistance and processing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If LDPE is used to achieve good TD shrinkage, then transverse direction shrinkage is improved, but mechanical strength and stiffness are compromised
Solution Approach 1:
The patent applies composite materials by combining LDPE and LLDPE in a multi-layer coextruded film structure. The LDPE layer (5-50 wt%) provides the necessary TD shrinkage properties, while the LLDPE layer (50-95 wt%) contributes mechanical strength and stiffness. This composite approach allows the film to achieve both good shrinkage behavior and adequate mechanical properties, resolving the contradiction between these two opposing requirements.
2Strength
If multimodal polyethylene formulations are used to improve performance, then most key attributes are enhanced, but TD shrinkage is compromised
Solution Approach 1:
The patent applies local quality by creating a multi-layer film structure where different polymer compositions are assigned to different layers. The LDPE-rich layer (5-50 wt%) is specifically positioned to provide TD shrinkage, while the LLDPE-rich layer provides mechanical strength. This localized functional distribution allows each layer to optimize its specific property, ensuring the film achieves both good TD shrinkage and enhanced mechanical attributes simultaneously.
3Shape
If large blow ratio is used to achieve TD orientation, then transverse direction shrinkage is improved, but waste increases
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition parameters of the film rather than relying on extreme mechanical processing parameters like large blow ratios. By adjusting the LDPE content (5-50 wt%) and using coextrusion technology, the film achieves adequate TD shrinkage through material composition control. This approach reduces waste by avoiding excessive material loss associated with high blow ratio processing while still achieving the desired TD orientation and shrinkage properties.
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 addition of COC significantly improves TD shrinkage and stiffness balance, maintaining excellent optical properties and enabling potential downgauging opportunities, thus enhancing the performance and efficiency of polyethylene films in shrink wrap applications.
Implementation Method 1
wherein the cyclic olefin copolymer has a glass transition temperature (Tg) of at least 80, or 90, or 100° C.
Implementation Method 2
Due to its long chain branching, the polymer can be easily oriented during the blown film process resulting in the desired shrink properties
Implementation Method 3
MD shrink is typically acceptable, as the majority of the orientation of the blown film occurs in the machine direction
Data Source
AI summary
A film, preferably, a multi-layered film, including a polymer composition, wherein the polymer composition includes: within a range from 1 wt % to 25 wt % of a cyclic olefin copolymer based on the weight of the polymer composition, and within a range from 75 wt % to 99 wt % (the remainder of material) of a polyethylene based on the weight of the polymer composition, wherein the cyclic olefin copolymer has a glass transition temperature (T.sub.g) of at least 80.degree. C. The films may be used in shrink packaging application.