HDPE and Cyclic Olefin Copolymer Blend for High Stiffness Caps
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Solution Overview
Problem
Current polyethylene blends for injection and compression molded caps and closures lack sufficient tensile modulus while maintaining processability and avoiding shrinkage and stress crack resistance issues, particularly in thinner designs required for weight reduction.
Innovation Solution
A bimodal high-density polyethylene (HDPE) blended with a cyclic olefin copolymer (COC) at specific weight ratios, enhancing tensile modulus without compromising stress crack resistance or causing shrinkage, using COC's high tensile modulus and amorphous properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If HDPE is used for cap production to maintain processability and stress crack resistance, then processability and ESCR are preserved, but tensile modulus is limited around 900 MPa
Solution Approach 1:
The patent applies composite materials by blending HDPE with COC (cyclic olefin copolymer) to create a new polymer composition. The COC component contributes high tensile modulus (typically 2000-3000 MPa) while the HDPE maintains processability and stress crack resistance. This composite approach allows achieving tensile modulus >1000 MPa while preserving the beneficial properties of HDPE.
2Strength
If HDPE is used for cap production, then stress crack resistance is maintained, but tensile modulus is limited and cannot exceed 900 MPa
Solution Approach 1:
The patent uses composite materials by combining HDPE (providing stress crack resistance) with COC (providing high tensile modulus). The synergistic effect of this composite allows achieving tensile modulus >1000 MPa while maintaining FNCT ≥ 30 hours, resolving the contradiction between strength and reliability.
3Strength
If COC is blended with HDPE to improve tensile modulus, then stiffness increases, but shrinkage and warpage may occur
Solution Approach 1:
The patent applies parameter changes by optimizing the composition ratio of HDPE and COC, controlling COC content within 5-20 wt%. This parameter optimization ensures that the tensile modulus increases to >1000 MPa while shrinkage remains controlled at ≤ 2%. The patent also optimizes processing parameters like injection temperature and pressure to minimize warpage and shrinkage.
4Weight of moving object
If thinner caps are produced to reduce weight, then weight savings are achieved, but mechanical performance and stiffness are compromised
Solution Approach 1:
The patent uses composite materials (HDPE+COC blend) with high tensile modulus to produce thinner caps that maintain mechanical performance. The COC component's high stiffness allows reducing cap thickness while maintaining required mechanical properties, achieving weight reduction without compromising strength.
Solution Approach 2:
The patent applies parameter changes by optimizing the polymer composition to achieve tensile modulus >1000 MPa, which enables producing thinner caps with sufficient mechanical performance. The optimized composition allows reducing wall thickness while maintaining stiffness and strength requirements.
Data Source
AI summary
A polymer composition comprising: (C) at least 80 wt% of a multimodal high density polyethylene having a density of 940 kg/m3 or more; and (D) 1 to 14 wt% of a cyclic ethylene copolymer or cyclic propylene copolymer.