Silane-Crosslinkable Polyethylene Rheology for Seal Extrusion

The patent applies parameter changes by modifying the molecular weight distribution through controlled radical treatment. This changes the MFR from a single parameter to a distributed parameter system, where the gel fraction (5-60%) becomes a key controlling parameter that simultaneously influences both softness/compression set and extrusion processability. The molecular weight enlargement through radical treatment creates a tailored molecular architecture that resolves the contradiction between low MFR (for softness) and extrusion suitability.

The patent creates a composite molecular structure within the polyethylene composition by forming gel phases through radical treatment. This composite structure consists of crosslinked gel networks embedded in the polymer matrix, creating a heterogeneous material system where the gel fraction (5-60%) provides the desired mechanical properties while the remaining matrix maintains processability. This composite approach allows simultaneous achievement of low compression set and good extrusion characteristics.

The patent transforms the molecular weight parameter from a uniform high value to a distributed system characterized by gel fraction (5-60%) and molecular weight distribution. The radical treatment creates a specific molecular architecture where molecular weight enlargement is controlled and distributed, preventing excessive viscosity while achieving desired softness. The key is controlling the gel fraction range rather than simply increasing average molecular weight.

The patent applies partial action by performing radical treatment to a controlled extent, creating a gel fraction of 5-60% rather than complete crosslinking. This partial molecular weight enlargement achieves the necessary softness improvement while leaving sufficient uncrosslinked polymer chains to maintain acceptable melt viscosity for extrusion. The treatment is applied just enough to achieve the target gel fraction without excessive crosslinking that would prevent processing.

The patent changes the crosslinking parameter from a simple degree metric to a gel fraction parameter (5-60%) that better characterizes the network structure. The radical treatment creates a specific gel structure where the gel fraction becomes the controlling parameter for both compression set and melt elasticity. This parameter transformation allows independent optimization of mechanical properties and rheological behavior.

The patent applies local quality by creating localized gel structures distributed throughout the polymer matrix rather than uniform crosslinking. The radical treatment generates discrete crosslinked regions (gel phases) with specific properties embedded in the continuous polymer matrix. This local crosslinking approach allows the material to exhibit low compression set in the gel regions while maintaining appropriate melt elasticity in the overall system for profile formation.