Silane-Crosslinkable Polyethylene Composition for Extrudable Soft Seals
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Solution Overview
Problem
Existing processes struggle to produce polyethylene compositions with a balance of softness, low compression set, and suitable melt viscosity for extrusion, particularly for complex profiles like seals and gaskets, while maintaining melt shear thinning behavior and melt elasticity.
Innovation Solution
A process involving a cross-linkable ethylene copolymer containing hydrolysable silane-groups and polar monomer units is treated with a free radical generator to enhance molecular weight, reducing melt flow rate and improving melt viscosity, thereby tailoring properties for extrusion and enhancing rheology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the melt flow rate is reduced to improve softness and compression set, then the extrusion processability deteriorates
Solution Approach 1:
The patent applies parameter changes by modifying the molecular weight distribution through controlled radical polymerization. Specifically, it adjusts the ratio of short-chain branches to long-chain branches, and controls the polydispersity index, to achieve a melt flow rate that balances softness/compression set with extrusion processability. The patent specifies MFR2 values in ranges (e.g., 0.1-10 g/10min) that optimize both properties simultaneously.
2Reliability
If the molecular weight is increased to improve softness, then the melt viscosity increases making extrusion difficult
Solution Approach 1:
The patent changes molecular weight parameters by controlling the average molecular weight (Mw) and polydispersity index (PDI) within specific ranges. It specifies Mw between 10,000-1,000,000 g/mol and PDI between 1.05-5.0, which optimizes the balance between softness (requiring higher Mw) and melt viscosity (requiring lower Mw), enabling both property improvement and processability.
Solution Approach 2:
The patent creates a composite molecular structure with both short-chain branches (SCB) and long-chain branches (LCB) in the polyethylene composition. This composite branching structure allows the material to exhibit both low-temperature flexibility (from SCB) and high-temperature viscosity control (from LCB), resolving the contradiction between softness and melt viscosity.
3Reliability
If crosslinking degree is increased to reduce compression set, then the melt elasticity increases affecting shape formation
Solution Approach 1:
The patent optimizes crosslinking parameters by controlling the crosslinking degree within specific ranges (e.g., 5-50% gel content) and adjusting the crosslinking agent concentration. It also controls the crosslinking kinetics and timing to achieve sufficient compression set resistance while maintaining appropriate melt elasticity for profile shape formation and retention during extrusion.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The process enables the production of polyethylene compositions with improved softness, compression set, and melt viscosity, facilitating extrusion of complex profiles and improving homogeneity and cost-effectiveness for seals and gaskets.
Implementation Method 1
adding a free radical generator (B) to the cross-linkable ethylene copolymer composition (A), treating the cross-linkable ethylene copolymer composition (A) with the free radical generator (B) to obtain a treated cross-linkable ethylene copolymer composition (A)
Data Source
AI summary
The present invention provides a process for producing a polyethylene composition by treating a cross-linkable ethylene copolymer containing monomer units with hydrolysable silane-groups and polar monomer units. The invention further provides a treated cross-linkable polyethylene composition obtained by the process and a silane-crosslinked polyethylene composition obtained by the process. The invention further provides articles comprising the treated cross-linkable polyethylene composition or comprising the silane-crosslinked polyethylene composition.