Polypropylene Composition for Low Sealing Temperature and Haze Control
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Solution Overview
Problem
Current polypropylene compositions for heat sealing applications face challenges in achieving a balance between low sealing initiation temperature, beneficial optical properties, and low xylene cold soluble content, often compromising one property for another, such as high comonomer content leading to lower melting temperatures and increased overall migration.
Innovation Solution
A polypropylene composition comprising a blend of 60.0 to 95.0 wt.% metallocene-catalysed propylene-hexene random copolymer and 5.0 to 40.0 wt.% Ziegler-Natta catalysed propylene-ethylene random copolymer, with specific ranges for 1-hexene content, MFR, melting temperature, and xylene cold soluble amounts, which surprisingly achieves a lower sealing initiation temperature than individual components and improved optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If higher comonomer content is used to improve sealing behaviour (lower SIT), then sealing initiation temperature decreases, but melting temperature decreases and overall migration increases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the comonomer content (1.0-5.5 wt.% hexene, 0.5-8.0 wt.% ethylene) and catalyst type to achieve the optimal balance between sealing initiation temperature and overall migration. This resolves the contradiction by finding the specific parameter range where low SIT is achieved without excessive migration.
Solution Approach 2:
The patent uses a composite material approach by blending metallocene-catalysed propylene-hexene random copolymer (60.0-95.0 wt.%) with Ziegler-Natta catalysed propylene-ethylene random copolymer (5.0-40.0 wt.%). This composite structure allows the composition to achieve low SIT through the metallocene component while the Ziegler-Natta component controls migration, resolving the contradiction between sealing performance and migration resistance.
2Temperature
If higher comonomer content is used to lower melting temperature for better sealing, then sealing behaviour improves, but xylene cold soluble content increases
Solution Approach 1:
The patent controls the comonomer content within specific ranges (hexene: 1.0-5.5 wt.%, ethylene: 0.5-8.0 wt.%) and selects appropriate catalysts to achieve the desired melting temperature while minimizing xylene cold soluble content. This parameter optimization resolves the contradiction between melting temperature and XCS content.
Solution Approach 2:
The blend composition combines metallocene-catalysed propylene-hexene random copolymer (providing low melting temperature) with Ziegler-Natta catalysed propylene-ethylene random copolymer (providing low XCS content). This composite approach allows simultaneous achievement of low melting temperature and low XCS content, resolving the contradiction.
3Temperature
If propylene-hexene random copolymer with low melting temperature is used to improve sealing, then sealing initiation temperature decreases, but optical properties (haze) worsen
Solution Approach 1:
The patent creates a composite material system where metallocene-catalysed propylene-hexene random copolymer (60.0-95.0 wt.%) provides low melting temperature and sealing performance, while Ziegler-Natta catalysed propylene-ethylene random copolymer (5.0-40.0 wt.%) contributes to improved optical properties. This composite structure resolves the contradiction between sealing temperature and haze.
Data Source
AI summary
Polypropylene composition which combines low sealing initiation temperature (SIT), low xylene cold soluble (XCS) content and thus low overall migration and good optical properties, like low haze. The present invention is furthermore related to the use of the polypropylene composition and articles, especially films made therefrom.