Polyethylene Composition for Injection-Moulded Pipe Fittings
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Solution Overview
Problem
Current polyethylene compositions for injection molding of pipe fittings lack improved mechanical properties such as slow crack growth resistance and rapid crack propagation resistance, which are crucial for long-term performance under internal pressure.
Innovation Solution
A polyethylene composition comprising a base resin with a first ethylene homo- or copolymer component and a second ethylene homo- or copolymer component, optionally with carbon black and additives, where the weight ratio of the components is optimized to achieve specific melt flow rates and molecular weights, enhancing both rheological and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a polymer suitable for extrusion is used for injection moulding, then the rheological properties may be inappropriate, but the mechanical properties can be insufficient
Solution Approach 1:
The patent uses a composite polymer system consisting of a polyethylene matrix combined with a specific elastomer blend (EPDM and EPM). This composite structure allows the material to exhibit both the rigidity and pressure resistance needed for PE100 mechanical properties and the elasticity and flow characteristics needed for successful injection moulding. The elastomer components modify the rheological behavior while the polyethylene matrix maintains the structural integrity and mechanical strength.
2Productivity
If instant cooling is applied during injection moulding to fill the cavity, then the filling speed improves, but internal stress increases causing stress cracking
Solution Approach 1:
The patent modifies the thermal and rheological parameters of the polymer composition by incorporating elastomers with specific glass transition temperatures and molecular weights. This allows the material to maintain lower viscosity at processing temperatures for rapid filling, then undergo controlled solidification with reduced thermal gradients. The composition parameters are tuned to enable faster cooling rates without generating excessive internal stresses that would cause cracking.
3Manufacturing precision
If packing pressure is applied to ensure complete filling, then the filling completeness improves, but shrinkage of the resultant article increases
Solution Approach 1:
The elastomer modification creates local regions of enhanced flexibility and shock absorption within the polymer matrix. During packing, these elastomeric domains allow for more uniform stress distribution and reduced localized compression. This enables complete cavity filling at lower packing pressures, thereby reducing overall shrinkage while maintaining dimensional accuracy and preventing void formation.
Data Source
AI summary
The present invention relates to a polyethylene composition comprising - a base resin comprising (A) a first ethylene homo- or copolymer component having a melt flow rate MFR2 (2.16 kg, 190℃) of equal to or more than 150g/10 min to equal to or less than 300 g/10 min, determined according to ISO 1133, and (B) a second ethylene homo- or copolymer component, - optional carbon black, - optional further polymer component(s) different to the first ethylene homo- or copolymer components (A) and (B), and - optional additive(s); wherein the first ethylene homo- or copolymer component (A) has a lower weight average molecular weight as the second ethylene homo- or copolymer component (B), and the weight ratio of the first ethylene homo- or copolymer component (A) to the second ethylene homo- or copolymer component (B) is from 40:60 t0 47:53; the polyethylene composition has a melt flow rate MFR5 (5 kg, 190℃) of equal to or more than 0.35 g/10 min to equal to or less than 0.60 g/10 min,determined according to ISO 1133. The invention further relates to a process for the production of such a polyethylene composition, an article, such as a pipe or pipe fitting comprising such a polyethylene composition and the use of such a polyethylene composition for the production of such an article.