Foamed Polyethylene Film Multimodal LLDPE LDPE Composition
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Solution Overview
Problem
Foamed polyethylene films and sheets face challenges such as the 'orange peel' effect and reduced mechanical properties due to uneven cell distribution and size, making them unsuitable for packaging applications, where a polymer with excellent melt strength and even cell structure is required.
Innovation Solution
A combination of broad molecular weight distribution multimodal linear low density polyethylene (LLDPE) with low density polyethylene (LDPE) provides the necessary melt strength and stretchability, allowing for the formation of foamed articles with even cell structures and improved mechanical properties, using a composition of 35 to 90 wt% LLDPE, 10 to 50 wt% LDPE, and 0.1 to 15 wt% foaming agent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If foaming is used to reduce film density and plastic usage, then weight reduction and cost savings are achieved, but the surface becomes rough with orange peel effect
Solution Approach 1:
The patent changes the molecular weight distribution parameters of the polyethylene from conventional narrow or unimodal distributions to broad multimodal distributions. This parameter change allows the polymer to form a smooth surface during foaming while maintaining the density reduction benefits, resolving the contradiction between weight reduction and surface smoothness.
Solution Approach 2:
The patent uses composite polymer systems combining polyethylene with specific molecular weight characteristics and foaming agents. This composite approach enables the material to exhibit both the lightness of foamed structures and the surface smoothness required for packaging applications, simultaneously achieving weight reduction and acceptable surface quality.
2Weight of stationary object
If smaller thicknesses are used in foamed films, then density reduction is improved, but mechanical properties drop seriously
Solution Approach 1:
The patent modifies the molecular weight distribution parameters to broad multimodal distributions, which fundamentally changes the mechanical behavior of the foamed film. This parameter change enables thin-walled foamed structures to maintain adequate mechanical strength by providing a wider range of molecular weights that contribute to both foam formation and structural integrity.
3Ease of manufacture
If conventional foamed polyethylene is used, then foaming process is simple, but cell distribution is uneven and cell size is inconsistent
Solution Approach 1:
The patent changes the molecular weight distribution from conventional narrow distributions to broad multimodal distributions. This parameter change improves cell structure uniformity by providing a wider range of molecular weights that contribute to more consistent foam cell formation, while maintaining relatively simple foaming processes.
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 LLDPE/LDPE composition enables the production of foamed films and sheets with enhanced mechanical properties and processability, achieving a uniform cell structure and reduced density, suitable for packaging applications without the need for additional additives like talc, while maintaining cost-effectiveness.
Implementation Method 1
At a high enough temperature and under pressure, the foaming agent will dissolve in the melted polymer and disperse
Implementation Method 2
At the exit of the die, when the pressure drops, the incompatibility of the gas in the polymer will create bubbles that are called cells
Implementation Method 3
As the polymer cools down to its solid phase, the growth of the cells is limited
Data Source
Figure 1
AI summary
A polymer composition comprising 35 to 89.9 wt% of a multimodal linear low density polyethylene (LLDPE) having an MFR21MFR2 of 50 to 200, 10 to 50 wt% of a low density polyethylene (LDPE) and 0.1 to 15.0 wt% of foaming agent component based on the total amount (100wt%) of the polymer composition.