Recyclable Multilayer Films with Polypropylene Blend Sealing Layers
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Solution Overview
Problem
Existing plastic packaging materials often require multiple polymer types to achieve desired properties like stiffness, toughness, and sealing, complicating recycling efforts, while single-material solutions limit property optimization and recyclability.
Innovation Solution
A multilayer film composed of a skin layer, core layer, and a sealing layer, where each layer is predominantly polypropylene, with the sealing layer containing a blend of random-heterophasic propylene-ethylene copolymer, first, and second propylene-ethylene random copolymers, optimizing mechanical, optical, and sealing properties while facilitating recycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple polymer types are used in multilayer films to achieve desired mechanical and sealing properties, then the film performance is improved, but the complexity of recycling increases
Solution Approach 1:
The film is divided into multiple layers (skin layer, core layer, sealing layer) with each layer serving a specific function. The skin layer provides mechanical strength and optical properties, the core layer provides toughness and puncture resistance, and the sealing layer provides sealing performance. This segmentation allows optimization of each layer's properties while maintaining overall film performance, and the use of compatible polymers in each layer facilitates recycling.
Solution Approach 2:
The patent uses different polymer grades with specific parameter ranges (melt flow rate, molecular weight, composition) in each layer to achieve the desired balance between performance and recyclability. By carefully selecting parameters within specified ranges, the film achieves optimal mechanical properties and sealing behavior while using polymers that can be effectively recycled together.
2Ease of manufacture
If a single polymer type is used to simplify recycling, then recyclability is improved, but the range of available properties is limited
Solution Approach 1:
The patent creates a composite structure where multiple polymer grades are combined in a multilayer configuration. Each layer uses polymers with specific properties optimized for its function, creating a composite material system that achieves a broader range of properties than any single polymer could provide alone, while maintaining recyclability through the use of compatible polymer types.
Solution Approach 2:
The multilayer film structure allows a single packaging component to fulfill multiple functions: the skin layer provides barrier and optical properties, the core layer provides mechanical strength and puncture resistance, and the sealing layer provides heat sealing capability. This multi-functionality is achieved within a recyclable single-polymer-type system by optimizing the composition and thickness of each layer.
3Strength
If high stiffness is achieved through polymer selection, then mechanical strength is improved, but toughness and sealing behavior may be compromised
Solution Approach 1:
Different layers of the film are assigned different quality characteristics optimized for their specific functions. The skin layer uses polymers with higher stiffness for structural integrity, while the core layer uses polymers with higher toughness for puncture resistance, and the sealing layer uses polymers optimized for sealing behavior. This local optimization of quality allows the overall film to achieve all required properties without compromise.
Data Source
AI summary
A multilayer film (F), comprising, in the given order, the following layers: (A) a skin layer; (B) a core layer; and (C) a sealing layer, comprising at least 90 wt.-% of a polypropylene composition (PC) comprising the following components: i) 20 to 70 wt.-% of a RAHECO having an MFR2 of 0.1 to 10.0 g/10 min; ii) 10 to 50 wt.-% of a first propylene-ethylene random copolymer (R-PP1) having an MFR2 of 1.0 to 6.0 g/10 min; and iii) 10 to 50 wt.-% of a second propylene-ethylene random copolymer (R-PP2) having an MFR2 of 7.0 to 20 g/10 min.