Tethered Bottle Closure Polyethylene Composition
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Solution Overview
Problem
Existing bottle closure systems face challenges in manufacturing due to complex molding processes and require materials with good stress crack resistance and flexibility to securely attach and detach cap portions without losing them.
Innovation Solution
A bottle closure assembly made from a polyethylene composition comprising 10-70 wt% of a first ethylene copolymer with a melt index of less than 1.0 g/10min and 90-30 wt% of a second ethylene copolymer or homopolymer, with specific density and short chain branch ratios, providing tensile elongation, strength, and processability for integrally molded cap, tether, and retaining collar portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyethylene composition is used for integrally molded tethered closure systems with long flow paths, then the molding process becomes more complicated and longer, but the material needs to maintain good processability and stress crack resistance
Solution Approach 1:
The patent uses a composite polyethylene composition combining two different polyethylene resins: a first polyethylene resin with high stress crack resistance (ESCR ≥ 1000 hours) and a second polyethylene resin with good processability (melt index 2.0-10.0 g/10min). This composite material simultaneously achieves both stress crack resistance and molding processability in integrally molded tethered closure systems with complex flow paths
Solution Approach 2:
The patent optimizes specific parameters of the polyethylene composition including the ratio of the two resins (first resin 30-70 wt%, second resin 70-30 wt%), molecular weight distribution (Mw/Mn ≤ 3.0), and density (0.940-0.965 g/cm³). These parameter changes enable the material to exhibit both good processability for complex mold flow paths and sufficient stress crack resistance for the tether portion
2Strength
If the tethering portion is made strong enough to prevent loss of the cap portion, then the material needs high strength, but it also needs to be flexible enough to be formed or bent into suitable closure system designs
Solution Approach 1:
The patent adjusts the molecular weight distribution (Mw/Mn ≤ 3.0) and density (0.940-0.965 g/cm³) parameters of the polyethylene composition to achieve an optimal balance between strength and flexibility. The controlled molecular weight distribution provides sufficient tensile strength for the tether while maintaining flexibility for forming complex closure system designs
3Ease of manufacture
If simple one-piece closures are manufactured, then the process is simple, but tethered closure systems require more complicated and longer flow paths in the mold
Solution Approach 1:
The patent employs a composite polyethylene composition that enables integrally molding of complex tethered closure systems. The specific combination of two polyethylene resins with complementary properties allows the material to flow through complex mold paths while maintaining sufficient strength in the final molded product, thus enabling integration of complex designs with a single molding process
Data Source
Figure 1A~1C
Figure 2A~2B
Figure 3A~3B
AI summary
The present disclosure describes bottle closure assemblies which are made at least in part with a polyethylene composition having good flow properties and good resistance to environmentally induced stress cracking. The bottle closure assembly comprises a cap portion, an elongated tether portion and a retaining means portion. The retaining means portions engages a bottle neck or an upper portion of a bottle. The elongated tether portion connects at least one point on the cap portion to at least one point on the retaining means portion so as to prevent loss of the cap portion from a bottle.