Polyethylene Composition for Caps and Closures
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Solution Overview
Problem
Current polyethylene compositions for bottle closures face challenges in achieving high dimensional stability, organoleptic properties, and environmental stress crack resistance while maintaining low shear viscosity, especially in high-speed injection applications, due to issues with molecular weight distribution and comonomer content.
Innovation Solution
A polyethylene composition comprising a blend of two ethylene copolymers with specific molecular weight distributions, densities, and short chain branching ratios, produced using a dual reactor solution phase polymerization process with single-site catalysts, to enhance dimensional stability and processability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high density polyethylene resin is used to achieve sufficient cap strength and stiffness, then structural strength is improved, but shear viscosity increases making rapid production difficult
Solution Approach 1:
The patent applies parameter changes by precisely controlling the molecular weight distribution (Mw/Mn ratio between 2.0-7.0) and comonomer content (0.1-5.0 mol%) of the polyethylene resin. This optimization allows the material to achieve both high cap strength and low shear viscosity for rapid production, resolving the contradiction between structural strength and productivity.
2Strength
If conventional Ziegler-Natta or Phillips catalyst systems are used to produce high density polyethylene, then cap strength is improved, but low molecular weight polymer chains with high comonomer content are generated resulting in poor organoleptic properties
Solution Approach 1:
The patent employs parameter changes by precisely controlling the comonomer content (0.1-5.0 mol%) and molecular weight distribution (Mw/Mn of 2.0-7.0) through single-site catalyst systems. This prevents the formation of low molecular weight chains with excessive comonomer content, thereby maintaining both cap strength and organoleptic properties.
Solution Approach 2:
The patent substitutes conventional Ziegler-Natta or Phillips catalyst systems with single-site catalyst systems (metallocene or constrained geometry catalysts). This replacement eliminates the production of harmful low molecular weight polymer chains while maintaining high density and cap strength, thereby improving organoleptic properties.
3Object-generated harmful factors
If polyethylene resin is used for one-piece closures to improve organoleptic properties, then organoleptic properties are improved, but dimensional stability and resistance to anisotropic shrinkage deteriorate
Solution Approach 1:
The patent applies parameter changes by optimizing the molecular weight distribution (Mw/Mn of 2.0-7.0) and comonomer content (0.1-5.0 mol%) of the polyethylene resin. These controlled parameters enable the material to maintain dimensional stability and resist anisotropic shrinkage while preserving the organoleptic properties of polyethylene.
Data Source
AI summary
A dual reactor solution polymerization process gives high density polyethylene compositions containing a first ethylene copolymer and a second ethylene copolymer and which have high dimensional stability, excellent processability as well as good organoleptic properties and reasonable stress cracking resistance. The polyethylene compositions are suitable for compression molding or injection molding applications and are useful, for example, in the manufacture of caps and closures for bottles, and for example, in bottles containing non-pressurized liquids.