Multilayer Polyethylene Film Segmentation for Flex Crack Resistance
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Solution Overview
Problem
Large format bag-in-box packages experience defects such as pinholes during transportation, leading to material loss and increased costs due to the need for complex film structures and high raw material costs, which are not efficiently addressed by existing multilayer films.
Innovation Solution
A multilayer film comprising a first and second skin layer with densities of 0.912 g/cm3 or less and a core with a higher density, made predominantly of polyethylene, providing improved flex crack resistance and recyclability while maintaining a low bending stiffness and high polyethylene content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex multilayer film structures with multiple components are used to improve flex crack resistance, then flex crack performance is improved, but raw material costs increase and manufacturing complexity increases
Solution Approach 1:
The film structure is segmented into three distinct layers: an outer skin layer, an inner skin layer, and a core layer. Each layer serves a specific function - the skin layers provide flexibility and crack resistance while the core layer provides structural support and puncture resistance. This segmentation allows each layer to be optimized independently for its specific function, achieving high flex crack resistance without requiring complex multi-component materials.
Solution Approach 2:
Different regions of the film are assigned different material properties tailored to their specific functions. The skin layers use lower density polyethylene (density ≤ 0.912 g/cm³) to provide flexibility and crack resistance, while the core layer uses higher density polyethylene (density > 0.912 g/cm³) to provide structural support and puncture resistance. This local differentiation of material properties optimizes overall performance without increasing overall complexity.
2Reliability
If multiple plys are used to reduce pinhole defects, then reliability is improved, but material costs and labor costs increase
Solution Approach 1:
The invention uses a composite film structure where three layers of polyethylene with different density characteristics are combined to create a single integrated film that provides both flexibility and puncture resistance. The outer and inner skin layers use lower density polyethylene (≤ 0.912 g/cm³) for flexibility, while the core layer uses higher density polyethylene (> 0.912 g/cm³) for puncture resistance. This composite structure eliminates the need for multiple separate plys while achieving the same reliability benefits.
3Reliability
If non-polyethylene materials are used to achieve improved flex crack performance, then flex crack resistance is improved, but manufacturing equipment requirements and maintenance needs increase
Solution Approach 1:
The entire film structure is made from polyethylene materials, ensuring homogeneity in terms of material compatibility with standard polyethylene extrusion equipment. By using polyethylene for all three layers (skin layers with density ≤ 0.912 g/cm³ and core layer with density > 0.912 g/cm³), the invention maintains compatibility with existing manufacturing infrastructure while achieving superior flex crack performance through the optimized multilayer structure.
4Strength
If film structures with higher density materials are used to improve puncture resistance, then puncture resistance is improved, but flexibility and bendability deteriorate
Solution Approach 1:
The film is segmented into functional zones: the core layer uses higher density polyethylene (> 0.912 g/cm³) to provide puncture resistance and structural support, while the outer and inner skin layers use lower density polyethylene (≤ 0.912 g/cm³) to provide flexibility and crack resistance. This segmentation allows each region to have the material properties optimized for its specific function, simultaneously achieving both puncture resistance and flexibility.
Solution Approach 2:
Different density characteristics are applied locally to different layers based on functional requirements. The core layer receives higher density material for puncture resistance, while the skin layers receive lower density material for flexibility. This local differentiation of material density optimizes both puncture resistance and flexibility without requiring a single uniform material throughout the entire film structure.
Data Source
AI summary
Embodiments of the present invention relate to multilayer films, bags, and other articles. In one aspect, a multilayer film comprises a first skin layer having an overall density of less than or equal to 0.912 g/cm3; a second skin layer having an overall density of less than or equal to 0.912 g/cm3; and a core positioned between the skin layers, wherein the core has an overall density that is at least 0.01 g/cm3 greater than then overall density of the first skin layer, wherein the overall density of the multilayer film is from 0.905 to 0.930 g/cm3, wherein the film has a bending stiffness of 1.35 mN·mm or less when the film has a thickness of 2 mils (50.8 microns), wherein the film exhibits a Gelbo flex crack performance of 2 pinholes or less in 20,000 cycles, and wherein the film comprises at least 95% by weight polyethylene based on the total weight of the film.