Polyolefin Film Composition for Low Seal Initiation Temperature
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Solution Overview
Problem
Conventional polyolefin compositions for extrusion coatings, films, and laminates face challenges such as lack of toughness, high seal initiation temperature, low hot tack, and processing difficulties due to narrow molecular weight distribution and high coefficients of friction.
Innovation Solution
A composition comprising a metallocene-catalyzed linear low density polyethylene (LLDPE) with a specific density and molecular weight distribution, combined with low density polyethylene (LDPE) to achieve improved properties like broad hot tack plateau, high tensile strength, low seal initiation temperature, and reduced neck-in, suitable for use in films, coatings, and laminates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional LDPE is used, then ease of extrusion and high melt strength are achieved, but toughness is lacking and seal initiation temperature is high
Solution Approach 1:
The patent uses a composite material system combining LDPE and LLDPE in specific ratios (30-70 wt% LDPE, 70-30 wt% LLDPE) to achieve both ease of extrusion from LDPE and improved toughness from LLDPE, resolving the contradiction between processability and mechanical strength
2Strength
If conventional LLDPE is used, then toughness and hot tack are improved, but processability is inhibited due to narrow molecular weight distribution
Solution Approach 1:
The patent changes the molecular weight distribution parameter of LLDPE to have a broader MWD (weight average molecular weight 100,000-500,000 g/mol, polydispersity index 2-10) while maintaining density and comonomer content, thereby improving processability while preserving toughness
3Temperature
If VLLDPE or plastomers with density less than 0.915 g/cm3 are used, then hot tack and seal initiation temperature are improved, but surface blocking and coefficients of friction increase
Solution Approach 1:
The patent adjusts the density parameter of the LLDPE component to be in the range 0.915-0.930 g/cm3, which is higher than VLLDPE but still provides low seal initiation temperature, while simultaneously reducing surface blocking and coefficients of friction for improved handling
4Temperature
If VLLDPE or plastomers with density less than 0.915 g/cm3 are used, then hot tack and seal initiation temperature are improved, but neck-in increases
Solution Approach 1:
The patent combines LLDPE (which provides hot tack) with LDPE (which provides high melt strength and resistance to neck-in) in a specific ratio, where the LDPE component compensates for the high neck-in tendency of low-density polyethylene, achieving both good hot tack and low neck-in
Data Source
AI summary
A polymeric composition that is suitable for use as a film or a coating. The polymeric composition comprises: (a) a first component comprising copolymer derived from ethylene and one or more C3 to C20 α-olefin comonomers. The first component has a density of about 0.911 to about 0.918 g/cm3, a compositional distribution breadth index (CDBI) of about 60% to about 85%, a melt index (MI) of about 16.0 to about 30.0 g/10 min, a molecular weight distribution (MWD) of about 1.5 to about 4.0, and a melt index ratio (MIR) of less than about 25; and (b) a second component comprising a low density polyethylene (LDPE). The second component has a g′ of about 0.8 to about 0.15 and a MI that is lower than the MI of the first component.