Polypropylene Composition for Extrusion Coating with High Melt Strength
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Solution Overview
Problem
Current polypropylene compositions for extrusion coating and foaming face challenges such as low melt strength, high gel content, and limited thermal stability, which restrict their use in high-demand applications like medical fields, and often require the addition of processing aids like LDPE or heterophasic materials.
Innovation Solution
A polypropylene composition with long chain branching and high strain hardening factor, produced using a single site catalyst and processed with peroxide and diene masterbatches, achieving high melt flow rates and low gel content without the need for LDPE or heterophasic materials, enabling improved processability and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If polypropylene is used for extrusion coating, then heat tolerance and transparency are improved, but processability deteriorates due to high neck-in and low maximum coating speed
Solution Approach 1:
The patent changes the molecular structure parameters of polypropylene by introducing long chain branches through controlled peroxide treatment and diene addition, transforming the polymer from linear to branched architecture. This structural parameter change enables the material to achieve both high heat tolerance and improved processability with reduced neck-in, resolving the contradiction between thermal performance and ease of operation
Solution Approach 2:
The patent creates a composite polypropylene system by combining peroxide-treated polypropylene with diene compounds (such as ethylene-propylene-diene copolymer). This composite approach allows the material to exhibit enhanced melt strength and reduced neck-in while maintaining heat tolerance, effectively resolving the processability issue without sacrificing thermal properties
2Productivity
If high melt flow rate is achieved through visbreaking with peroxide, then coating speed is improved, but gel content increases due to beta scission degradation
Solution Approach 1:
The patent introduces diene compounds as intermediary substances that mediate between peroxide treatment and the polypropylene chains. The dienes act as chain transfer agents that redirect the degradation pathway, preventing beta scission and gel formation while still allowing controlled molecular weight reduction for improved melt flow rate and coating speed
Solution Approach 2:
The patent converts the potentially harmful peroxide degradation reaction into a beneficial process by controlling the reaction conditions and adding dienes. The peroxide treatment, which would normally cause gelation through beta scission, is transformed into a useful chain scission process that reduces viscosity and improves processability while the dienes prevent harmful gel formation
3Ease of operation
If LDPE or heterophasic materials are added to improve processability, then coating speed is improved, but thermal stability deteriorates
Solution Approach 1:
The patent extracts and eliminates the need for LDPE or heterophasic materials as processing aids by fundamentally modifying the polypropylene molecular structure through peroxide treatment and diene addition. This extraction approach removes the thermal stability problem associated with mixed polymer systems while maintaining improved processability through the branched polypropylene structure
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 resulting polypropylene composition exhibits enhanced melt strength, drawability, and thermal stability, allowing for high-speed extrusion coating and foaming with reduced gel content, making it suitable for diverse substrates and applications, including medical and packaging uses.
Implementation Method 1
produced using a single site catalyst
Implementation Method 2
processed with peroxide and diene masterbatches
Data Source
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AI summary
The present invention relates to a polypropylene composition suitable for extrusion coating or extrusion foaming for a broad variety of substrates having high melt strength and drawability, excellent processability, low gel content, and being capable of withstanding high temperatures, a process for the provision of such polypropylene compositions and extrusion coated or extrusion foamed articles. The polypropylene composition comprises a polypropylene base resin whereby the polypropylene base resin has a MFR (2.16 kg, 230 °C, ISO 1133) of 5 to 35 g/10min and an optical gel index of 1000 or less, measured with an OCS gel counting apparatus on thin cast films with a film thickness of 70 µm which were produced with a chill roll temperature of 40 °C, whereby the polypropylene base resin has a strain hardening factor (SHF) of 2.3 to 7.0 when measured at a strain rate of 3.0 s-1 and a Hencky strain of 2.5. The process for the production of such a polypropylene composition is characterized in that a single site catalyst derived polypropylene intermediate base resin having a MFR (2.16 kg, 230 °C, ISO 1133) of 6.0 g/10min or lower is mixed with a peroxide masterbatch composition and an oligomeric diene masterbatch composition to form a pre-mixed material; and the pre-mixed material is melt mixed in a melt mixing device at a barrel temperature in the range of 180 to 300 °C