Propylene Copolymer BOPP Heat Seal Film
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Solution Overview
Problem
Biaxially oriented polypropylene (BOPP) heat seal layers face challenges in achieving low seal initiation temperature, low hexane solubles content, and improved optical properties while maintaining good hot tack and anti-stick properties, which are essential for food packaging and other applications.
Innovation Solution
A propylene-comonomer copolymer with a bimodal distribution of ethylene, produced using a bridged metallocene catalyst, which results in a copolymer with a melting temperature of at most 145°C, low hexane solubles content, and enhanced hot tack properties, allowing for improved sealing performance and optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the ethylene content in the propylene copolymer is increased to lower seal initiation temperature, then sealing performance is improved, but hexane solubles content increases which violates food packaging regulations
Solution Approach 1:
The patent applies segmentation by creating a bimodal comonomer distribution with two distinct populations: a first population with low ethylene content (0.1-3.0 wt%) that maintains low hexane solubles for food packaging compliance, and a second population with higher ethylene content (3.0-7.0 wt%) that provides the necessary sealing performance. This segmentation allows each population to fulfill its specific function without compromising the other requirements.
Solution Approach 2:
The patent implements local quality by ensuring that the comonomer distribution is not uniform throughout the polymer but rather has different local concentrations. The bimodal distribution creates regions with different ethylene contents, where low-ethylene regions provide structural integrity and low hexane solubles, while high-ethylene regions provide sealing capability. This local variation in composition resolves the contradiction between sealing performance and regulatory compliance.
2Temperature
If the comonomer content is increased to improve seal initiation temperature, then sealing performance is enhanced, but optical properties such as transparency and haze are degraded
Solution Approach 1:
The patent segments the comonomer content into two distinct populations with different ethylene concentrations. The first population (low ethylene: 0.1-3.0 wt%) maintains excellent optical properties including high transparency and low haze, while the second population (higher ethylene: 3.0-7.0 wt%) provides the necessary sealing performance. This segmentation allows the polymer to achieve both good optics and sealing without requiring high overall comonomer content.
3Productivity
If the melt flow rate is increased to improve processing, then manufacturing efficiency is enhanced, but heat seal layer thickness control becomes difficult leading to production issues
Solution Approach 1:
The patent changes the molecular weight distribution parameters by specifying a controlled MFI range of 0.5-10.0 g/10min and a molecular weight distribution ratio Mw/Mn of at least 1.7. These parameter changes ensure the polymer has appropriate viscosity for precise thickness control during extrusion while maintaining processability. The specific parameter ranges balance manufacturing efficiency with the ability to control heat seal layer thickness accurately.
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 propylene-comonomer copolymer achieves a balance of low seal initiation temperature, low hexane solubles, and superior hot tack properties, ensuring effective sealing and compliance with food packaging regulations, while maintaining high melting temperature and optical quality.
Implementation Method 1
a melting temperature, measured by differential scanning calorimetry, of at most 145°C
Data Source
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AI summary
The present invention provides a propylene-comonomer block copolymer having a molecular weight distribution Mw/Mn of at least 1.7; a percentage of enthalpy measured between Ti and [Tm-18 °C] of at least 20% of the total enthalpy, wherein the total enthalpy is determined by stepwise isothermal segregation technique SIST, Ti is the initial melting temperature and Tm is the melting temperature, and a ratio E1/Co of at least 0.80, wherein said ratio is determined by 13C-NMR analysis and is the molar fraction of ethylene comonomer in sequences of length 1 relative to the total comonomer content and wherein the sequences of length 1 correspond to the following structures (A) and/or (B) and/or (C), wherein R is the lateral chain appearing in the polypropylene chain after insertion of a comonomer other than ethylene, i.e. R is Cn H2n+1 wherein n is at least 2.