Crystalline Block Composite Tie Layers for Heat-Resistant Films
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Solution Overview
Problem
Conventional tie layers in multilayer films fail to maintain adhesion at high temperatures, leading to delamination and poor performance in applications such as retort packaging due to issues in the maleic anhydride grafting process, where polypropylene undergoes chain scission and grafting occurs on shorter oligomers rather than the polymer backbone.
Innovation Solution
Incorporation of a crystalline block composite (CBC) component and functionalized polyethylene in tie layers, comprising ethylene polymer, alpha-olefin-based crystalline polymer, and a block copolymer, with functionalized polyethylene grafted with ethylenically unsubstituted dicarboxylic acid, to enhance adhesion and heat resistance up to 120°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If maleic anhydride grafting process is used on polypropylene, then adhesion to polar barrier layers is improved, but chain scission occurs and grafting happens on shorter oligomers rather than polymer backbone
Solution Approach 1:
The patent changes the chemical parameters of the grafting process by using functionalized polyethylene with specific density ranges (0.915-0.940 g/cm³) and controlled maleic anhydride content (0.5-3.0 wt%), along with specific processing conditions (temperature 180-220°C, residence time 2-5 minutes) to achieve effective grafting without excessive chain scission
Solution Approach 2:
The patent creates a composite tie layer formulation combining functionalized polyethylene with polypropylene and other additives, where the functionalized polyethylene component provides the necessary adhesion while the composite structure distributes stress and maintains overall polymer integrity
2Strength
If conventional polypropylene tie layer is used, then adhesion to polypropylene layers is maintained, but adhesion fails at high temperatures greater than 100°C
Solution Approach 1:
The patent changes the thermal parameters by selecting functionalized polyethylene with specific density and molecular weight characteristics, and controlling the maleic anhydride grafting level, which raises the effective service temperature from above 100°C to above 120°C while maintaining adhesion strength
Solution Approach 2:
The functionalized polyethylene acts as an intermediary material between the polypropylene layers and polar barrier layers, providing thermal stability and chemical reactivity that neither pure polypropylene nor polar polymers possess alone, enabling high-temperature adhesion
3Strength
If maleic anhydride grafting is increased to improve adhesion, then adhesion strength increases, but delamination occurs during storage and heat processing
Solution Approach 1:
The patent optimizes the maleic anhydride content parameter within a specific range (0.5-3.0 wt%) and controls the density of functionalized polyethylene (0.915-0.940 g/cm³), achieving sufficient adhesion strength while preventing the excessive crosslinking and brittleness that cause delamination during storage and processing
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 CBC component and functionalized polyethylene provide superior adhesion enhancement and improved heat resistance, ensuring multilayer film integrity during high-temperature applications.
Implementation Method 1
a polypropylene-based matrix resin for diffusion to the adjacent polypropylene layer
Implementation Method 2
a maleic anhydride-grafted polypropylene for chemical reaction with EVOH or nylon
Implementation Method 3
provide improved heat resistance for high-temperature applications such as retort packages. Some embodiments of the present disclosure may be suitable for high temperature applications up to 120 °C
Data Source
AI summary
A multilayer film includes first and second outer layers including polypropylene, a core layer including at least one polar polymer disposed between the first outer layer and the second outer layer, a first tie layer disposed between the first outer layer and the core layer, and a second tie layer disposed between the first outer layer and the core layer, wherein the first tie layer, the second tie layer, or both include a crystalline block composite (CBC) component including an ethylene polymer (EP), an alpha-olefin-based crystalline polymer (CAOP) and a block copolymer including an ethylene polymer block and a crystalline alpha-olefin block (CAOB), functionalized polyethylene, wherein the functionalized polyethylene comprises polyethylene grafted with ethylenically unsubstituted dicarboxylic acid or derivative thereof; and at least one of a polyolefin elastomer, an ethylene propylene diene terpolymer, or an olefin block copolymer.