Ethylene Copolymers with Single-Site Catalysts for Packaging Films
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Solution Overview
Problem
Current polyethylene resins for packaging films lack a balance between film toughness, stiffness, creep resistance, and processability, with existing solutions either compromising on toughness and stiffness or exhibiting unsatisfactory creep performance.
Innovation Solution
Development of ethylene copolymers with specific density, molecular weight distribution, comonomer distribution, and melting behavior, produced using single-site catalysts, which provide improved creep resistance, high toughness, and good processability, and exhibit a uniform melting behavior with a single peak in DSC measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional polyethylene resins are used to achieve film toughness and stiffness, then film performance is improved, but creep resistance deteriorates
Solution Approach 1:
The patent changes the molecular weight distribution parameters by using single-site catalysts to produce ethylene copolymers with specific Mz/Mw ratios greater than 2, and controls comonomer distribution to achieve uniform melting behavior. These parameter changes result in improved creep resistance while maintaining film toughness and stiffness through optimized molecular architecture.
2Strength
If polyethylene resins are optimized for film toughness and stiffness, then mechanical performance is improved, but processability deteriorates
Solution Approach 1:
The patent optimizes molecular weight distribution parameters (Mz/Mw > 2) and comonomer distribution using single-site catalysts to achieve uniform melting behavior. This allows the resin to maintain high film stiffness while improving processability through better melt flow characteristics and reduced processing temperatures.
3Reliability
If uniform melting behavior is achieved through single-site catalysis, then creep resistance is improved, but molecular weight distribution control becomes more difficult
Solution Approach 1:
The patent specifies target Mz/Mw ratios greater than 2 and controls comonomer distribution parameters to achieve uniform melting behavior. By setting these specific parameter targets and using single-site catalysts with controlled comonomer incorporation, the patent simultaneously achieves improved creep resistance and manageable molecular weight distribution control.
Data Source
AI summary
Embodiments of the invention described herein relate to a polyethylene polymer composition suitable for use in the manufacture of packaging articles, flexible films and/or sheets. In one embodiment, the copolymer comprises a polyethylene resin with density 0.918 g/cm3 to about 0.935 g/cm3, G′ at G″(500 Pa) value, as determined from Dynamic Mechanical Analysis at 190° C., of less than 40 Pa, Mz/Mw of greater than 2, CDBI50 of greater than 60. Other embodiments relate to polymer compositions with defined molecular characteristics and formulations suitable for use in the manufacture of articles including films, sheets, bags and pouches with improved creep resistance and high toughness and a good balance of film stiffness and processability in monolayer and/or multi-layer film structures.