Uniaxially Oriented Multi-Layer Polyolefin Films for Stiffness and Tear Strength
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Solution Overview
Problem
Conventional machine direction oriented films face limitations in achieving significant downgauging while maintaining desirable mechanical properties such as tear strength and stiffness, often resulting in weak tear strength and fibrillation when stretched at high ratios.
Innovation Solution
A uniaxially oriented film comprising multiple layers, including a first layer with an ethylene-based polymer prepared using a single-site catalyst and Ziegler-Natta catalyzed ultra low density polyethylene, and an inner layer of high density polyethylene, oriented in the machine direction at a draw ratio of 4:1 to 10:1, achieving a high 2% secant modulus of 85,000 psi or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If machine direction oriented films are stretched at high draw ratios (6:1 to 10:1), then stiffness and optical properties are improved, but tear strength in the machine direction deteriorates due to fibrillation
Solution Approach 1:
The film is divided into multiple layers with different polyolefin compositions, where each layer contributes different properties. The first layer provides stiffness through high density polyethylene, while subsequent layers provide toughness and tear strength through lower density polyolefins, segmenting the functional requirements across different layers
Solution Approach 2:
The invention uses composite materials by combining multiple polyolefin layers with different density and mechanical properties. This composite structure allows the film to simultaneously achieve high stiffness in the machine direction and high tear strength, as each material component contributes its advantageous properties to the overall film performance
2Quantity of substance
If films are down gauged to achieve thinner packaging, then cost and weight are reduced, but mechanical properties such as toughness and tear strength deteriorate
Solution Approach 1:
The invention changes the compositional parameters of the film by using specific polyolefin blends with controlled density distributions. This allows the film to achieve enhanced mechanical properties at reduced thickness levels, as the material composition itself is optimized to provide strength without requiring excessive thickness
3Shape
If unidirectional orientation is applied to provide stiffness, then machine direction properties are improved, but cross direction tear strength deteriorates
Solution Approach 1:
The film structure segments different directional requirements into different layers, allowing machine direction stiffness and cross direction tear strength to be independently optimized through the specific polyolefin composition and layer arrangement
Solution Approach 2:
Different regions of the film (different layers) have different local qualities and properties. The first layer is optimized for machine direction stiffness, while subsequent layers are optimized for cross direction tear strength, creating local quality variations that satisfy different functional requirements
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 film exhibits a limited drop in tear strength and maintains high mechanical properties even after orientation, providing a balance of stiffness and toughness suitable for flexible packaging applications.
Implementation Method 1
the film is oriented in the machine direction at a draw ratio of between 4:1 and 10:1
Data Source
AI summary
The present invention provides uniaxially oriented films and packages formed from such films. In one aspect, a uniaxially oriented film includes (a) a first layer including (i) a first composition including an ethylene-based polymer prepared in the presence of a single-site catalyst, wherein the first composition has a density of 0.935 g/cm3 to 0.965 g/cm3, a melt index (12) of 0.5 to 6 g/10 minutes, and a MWD of 6.0 or less, and (ii) a Ziegler-Natta catalyzed ultra low density polyethylene having a density of 0.880 g/cm3 to 0.912 g/cm3, a melt index (12) of 0.5 to 6 g/10 minutes, and a MWD of 6.0 or less, (b) a second layer including at least one polyolefin, and (c) at least one inner layer between the first layer and the second layer including a high density polyethylene. The film is oriented in the machine direction at a draw ratio of between 4:1 and 10:1, and can exhibit a machine direction 2% secant modulus of 85,000 psi or more when measured as per ASTM D882.