Multilayer Thermoplastic Film Puncture Resistance via Segmentation
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Solution Overview
Problem
Current heat shrink films for packaging, particularly those used for food and industrial goods, face challenges in achieving a balance between high puncture resistance, wide orientation windows, and high modulus, which are essential for effective packaging and handling, but these properties are often mutually exclusive due to limitations in resin properties and fabrication processes.
Innovation Solution
A biaxially stretched, multilayer thermoplastic film is developed with a puncture-resistant layer composed of a polyethylene-based plastomer with specific density, molecular weight distribution, and comonomer distribution, optimized for a broad orientation window and high puncture resistance, along with additional layers for enhanced properties, processed using a double-bubble technique.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If oriented polyolefin film is stretched to achieve high shrink response, then puncture resistance decreases due to orientation constraints
Solution Approach 1:
The film is divided into multiple layers with different functions: a puncture-resistant layer (higher density polyolefin) and a shrink-responsive layer (lower density polyolefin). This segmentation allows each layer to optimize for its specific function without compromising the other, resolving the contradiction between puncture resistance and shrink response.
Solution Approach 2:
The invention uses composite multilayer structures combining different polyolefin types (ULDPE, LLDPE, LDPE) with distinct density and molecular weight characteristics. The composite structure integrates the high puncture resistance of higher density layers with the high shrink response of lower density layers, achieving both properties simultaneously.
2Strength
If film density is increased to improve puncture resistance, then shrink response decreases due to crystallite constraints
Solution Approach 1:
The film structure segments density functions across layers: higher density (0.920-0.940 g/cm³) in the puncture-resistant layer and lower density (0.910-0.920 g/cm³) in the shrink-responsive layer. This resolves the contradiction by assigning opposite density requirements to different functional layers.
Solution Approach 2:
Different regions of the film have different density qualities optimized for their specific functions. The puncture-resistant layer has higher density locally optimized for strength, while the shrink layer has lower density locally optimized for elasticity and shrinkage, resolving the global contradiction through local optimization.
3Strength
If molecular weight is increased to improve puncture resistance, then processing difficulty increases
Solution Approach 1:
The invention optimizes molecular weight parameters within specific ranges (Mw/Mn of 2.0-4.0, Mz/Mw of 2.0-3.0) to balance puncture resistance and processability. These parameter changes ensure the polymer has sufficient strength while maintaining adequate melt flow for fabrication processes.
Solution Approach 2:
The invention utilizes the phase transition behavior of polyolefins during processing, selecting molecular weight distributions that provide appropriate melt viscosity at processing temperatures while maintaining solid-state strength. The molecular weight parameters are optimized to ensure proper phase transition characteristics for both fabrication and end-use performance.
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 multilayer film achieves improved puncture resistance, expanded orientation window, and high modulus, enabling better handling and packaging performance while maintaining shrink response, suitable for food and industrial applications.
Implementation Method 1
biaxially stretched
Implementation Method 2
Subsequent application of heat will then cause the oriented film to relax and, depending on the actual shrink temperature, the oriented film can return essentially back to its original unstretched dimensions
Implementation Method 3
the oriented film can return essentially back to its original unstretched dimensions, i.e., to shrink relative to its stretched dimension
Data Source
AI summary
The present disclosure provides for a heat-shrinkable, biaxially stretched, multilayer thermoplastic film that includes at least a puncture resistant layer. The puncture resistant layer is formed with a polyethylene based plastomer having a density of 0.890 g/cm3 to 0.910 g/cm3 as measured in accordance with ASTM D-792, and a melt index (MI) as measured by ASTM D-1238 at 190° C./2.16 kg from 0.20 g/10 minutes to 1.5 g/10 minutes. The polyethylene based plastomer has a logM25% of an upper 25% of a GPC quadrant having a value of 5.1 to 5.7, an intermediate molecular weight distribution (Mw/Mn) of 2.5 to 3, a Mz/Mw value of 2 to 2.5, a Comonomer Distribution Constant value from 60 to 400 and a single SCBD peak between 40-85° C. with a mass fraction of less than 3% above 85° C. as determined by CEF, and a ZSVR value from 1.0 to 5.5. The multilayer thermoplastic film is biaxially stretched at a temperature of 60° C. to 120° C. with a blow-up ratio from 2:1 to 10:1.