MDO Film Sealability via Multimodal LLDPE and Plastomer Blend
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Solution Overview
Problem
Machine direction-oriented (MDO) films made from polyethylene have high seal initiation temperatures and narrow sealing windows, making high-temperature sealing processes necessary, which can cause shrinkage and compromise mechanical properties.
Innovation Solution
A blend of multimodal linear low-density polyethylene (LLDPE) and a low-density plastomer is used in the sealing layer of MDO films, reducing seal initiation temperature and broadening the sealing window without significantly affecting mechanical properties like impact strength and tear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature sealing processes are used for MDO films, then sealing is achieved, but shrinkage occurs and mechanical properties are compromised
Solution Approach 1:
The patent changes the chemical composition parameters of the sealing layer by incorporating a blend of multimodal LLDPE and low-density plastomer (900 kg/m³). This compositional parameter change lowers the seal initiation temperature from typical high temperatures to below 105°C, enabling sealing at reduced temperatures that preserve the film's mechanical properties and prevent shrinkage.
Solution Approach 2:
The patent creates a composite sealing layer by blending two different polyethylene materials: multimodal LLDPE and low-density plastomer. This composite material combines the sealing characteristics of the plastomer with the mechanical strength contributions of the LLDPE, achieving a balance between sealability and mechanical performance in the sealing layer.
2Reliability
If single site LLDPE of low density is used in MDO film, then sealing performance improves in unstretched film, but seal initiation temperature is not lowered after MD stretching
Solution Approach 1:
The patent changes the density parameter of the plastomer component to specifically 900 kg/m³, which is lower than conventional LLDPE densities. This extreme parameter value ensures that even after machine direction stretching increases crystallinity, the seal initiation temperature remains below 105°C, overcoming the limitation of conventional low-density LLDPE that fails to maintain low sealing temperatures after orientation.
3Strength
If MD stretching is applied to increase crystallinity and mechanical strength, then mechanical properties improve, but sealing performance deteriorates due to increased crystallinity
Solution Approach 1:
The patent applies local quality by creating a sealing layer with distinct composition (blend of multimodal LLDPE and low-density plastomer) differentiated from the rest of the film structure. This localized compositional variation allows the sealing layer to have low crystallinity and low seal initiation temperature, while the overall film maintains high mechanical strength through the MDO process applied to the bulk material.
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 solution effectively lowers the seal initiation temperature and widens the sealing window, allowing for lower temperature sealing processes while maintaining high mechanical performance, such as dart drop impact strength and tear resistance.
Implementation Method 1
The MD stretching of the polymer increases the crystallinity of the material and that results in poorer sealing performance
Implementation Method 2
machine directional oriented (MDO) films made from polyethylene
Data Source
AI summary
A monolayer machine direction oriented film comprising a blend of a multimodal linear low density polyethylene (LLDPE) and a plastomer having a density of 900 kg/m3 or less, said film being a stretched film which is uniaxially oriented in the machine direction (MD) in a draw ratio of at least 1:3; or a multilayer machine direction oriented film comprising at least an (A) layer and (B) layer, said (A) layer being an outer layer and comprising a multimodal linear low density polyethylene (LLDPE) and a plastomer having a density of 900 kg/m3 or less; said (B) layer comprising a multimodal linear low density polyethylene (LLDPE); wherein said film is a stretched film which is uniaxially oriented in the machine direction (MD) in a draw ratio of at least 1:3.