LDPE Composition for Extrusion Coatings with Balanced Melt Strength
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Solution Overview
Problem
Conventional LDPE resins for extrusion coating have limitations due to lower density and melt strength, which restrict their use and do not provide benefits like reduced water vapor transmission and improved coefficient of friction, necessitating LDPE compositions with higher densities and good melt strength for enhanced performance.
Innovation Solution
A composition comprising two ethylene-based polymers formed through high-pressure free-radical polymerization processes, with specific melt index and density ranges, and a method for forming these compositions to achieve improved extrusion coatings with balanced adhesion and reduced substrate-polymer delamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If higher density LDPE is used for extrusion coating, then water vapor transmission is reduced and coefficient of friction is improved, but melt strength decreases
Solution Approach 1:
The patent uses a composite polymer system consisting of a first polyethylene polymer and a second polyethylene polymer with different density and molecular weight characteristics. This composite approach allows the formulation to achieve higher overall density (0.918-0.925 g/cc) while maintaining adequate melt strength through the synergistic combination of polymer components with complementary properties.
Solution Approach 2:
The patent systematically adjusts multiple parameters including polymer density (0.918-0.925 g/cc), melt index (2-10 g/10min), and molecular weight distribution to optimize both density-related benefits (water vapor transmission, coefficient of friction) and processing performance (melt strength, adhesion). By controlling the ratio and properties of the two polymer components, the formulation achieves the desired parameter balance.
2Ease of operation
If higher density LDPE is used for extrusion coating, then coefficient of friction is improved, but adhesion and substrate-polymer bonding may deteriorate
Solution Approach 1:
The patent employs a composite of two polyethylene polymers where the first polymer provides adhesion characteristics and the second polymer contributes to friction properties. This composite structure enables the simultaneous achievement of low coefficient of friction and good adhesion to substrate, resolving the trade-off between these two surface-related properties.
Solution Approach 2:
The patent creates different local properties within the polymer formulation by using two distinct polymer components with specialized characteristics. The first polymer is optimized for adhesion to substrate while the second polymer is optimized for friction properties, allowing each component to excel at its specific function within the composite system.
3Strength
If lower density LDPE is used to maintain melt strength, then processing is easier, but water vapor transmission increases and coefficient of friction worsens
Solution Approach 1:
The patent formulates a composite polymer system that decouples the relationship between density and melt strength. By combining a first polyethylene polymer with a second polyethylene polymer in specific ratios, the formulation achieves higher density (improving water vapor transmission resistance) while maintaining melt strength through the contribution of the first polymer component.
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 composition provides excellent extrusion coatings with improved neck-in and draw-down properties, maintaining substrate integrity, offering better moisture barrier, heat sealability, and mechanical strength, suitable for packaging without delamination or tearing.
Implementation Method 1
a first ethylene-based polymer, formed by a high pressure, free-radical polymerization process comprising at least one autoclave reactor, and a second ethylene-based polymer, formed by a high pressure, free-radical polymerization process comprising at least one autoclave reactor
Data Source
AI summary
The invention provides a composition comprising a first ethylene-based polymer, formed by a high pressure, free-radical polymerization process comprising at least one autoclave reactor, and a second ethylene-based polymer, formed by a high pressure, free-radical polymerization process comprising at least one autoclave reactor, such composition comprising the following properties: A) a melt index (I2) from 2.5 to 10 g/10 min; B) a density from 0.920 to 0.935 g/cc; and wherein the second polymer is present in an amount from 5 to 95 weight percent, based on the sum of the weight of the first polymer and the second polymer; and wherein the density of the of the second polymer is greater than the density of the first polymer, and wherein the first polymer has a melt index I2 greater than 2.5 g/10 min.