Extrusion Coating Polyethylene Composition for Web Stability
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Solution Overview
Problem
Extrusion coating processes face challenges such as edge waving, edge tear, web break, web stability, neck-in, and draw down limitations, which affect the quality and efficiency of polymer film application at high line speeds.
Innovation Solution
A polyethylene composition combining 70-98wt% high pressure low density polyethylene from a tubular reactor with 2-30wt% long chain branched low density polyethylene from an autoclave reactor, optimized for improved processability, web stability, and high draw down capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If tubular reactor LDPE is used for extrusion coating, then production rate and ethylene conversion rate are improved, but web stability and neck-in control deteriorate
Solution Approach 1:
The invention uses a composite polymer composition combining tubular reactor LDPE (70-98 wt%) with autoclave reactor LDPE (2-30 wt%). The tubular reactor component provides high productivity and cost-effectiveness, while the autoclave reactor component contributes broad molecular weight distribution and long chain branching that improve web stability and neck-in control. This composite approach allows simultaneous achievement of both productivity and web stability.
Solution Approach 2:
The invention changes the molecular structure parameters of the polymer by selecting specific reactor types and conditions. Tubular reactor LDPE has narrow molecular weight distribution and lower long chain branching, while autoclave reactor LDPE has broad molecular weight distribution and higher long chain branching. By controlling the ratio and properties of these two components, the composition achieves optimal rheological properties for both productivity and web stability.
2Ease of manufacture
If tubular reactor LDPE is used for extrusion coating, then production economics are improved, but neck-in increases
Solution Approach 1:
The composite composition combines cost-effective tubular reactor LDPE with autoclave reactor LDPE that has superior neck-in properties. The autoclave reactor component, though more expensive, is used in smaller amounts (2-30 wt%) to provide the necessary long chain branching and broad molecular weight distribution for low neck-in, while the majority tubular reactor component maintains production economics.
Solution Approach 2:
The invention applies local quality by having different polymer components perform different functions. The tubular reactor LDPE provides cost-effectiveness and basic coating properties, while the autoclave reactor LDPE specifically addresses the neck-in problem through its unique molecular structure with higher long chain branching. Each component contributes its strengths to the overall performance.
3Productivity
If high line speed is used in extrusion coating, then productivity is improved, but web break and edge stability deteriorate
Solution Approach 1:
The composite polymer composition provides enhanced melt strength and web stability at high line speeds. The autoclave reactor LDPE component with broad molecular weight distribution and long chain branching creates a more resilient melt structure that resists web break and maintains edge stability even at high processing speeds, enabling high productivity without sacrificing reliability.
Solution Approach 2:
The long chain branching in the autoclave reactor LDPE component creates a more spherical or branched molecular structure compared to linear polymers. This spherical-like branching structure entangles more effectively, providing better melt strength and web stability during high-speed extrusion coating, preventing web break and edge instability.
4Manufacturing precision
If high draw down is achieved, then coating quality is improved, but draw resonance and uneven coating weight occur
Solution Approach 1:
The invention optimizes the rheological parameters of the polymer melt by combining components with different molecular weight distributions. The broad molecular weight distribution of autoclave reactor LDPE provides shear thinning behavior that stabilizes the melt during draw down, reducing draw resonance and maintaining uniform coating weight while achieving high draw down ratios for quality coating.
Solution Approach 2:
The unique molecular structure of the composite composition provides self-regulating flow characteristics during extrusion. The long chain branching and broad molecular weight distribution create viscosity feedback that automatically adjusts to draw down conditions, preventing draw resonance and maintaining stable coating weight distribution even at high draw down ratios.
Data Source
AI summary
Extrusion coating polyethylene composition A), comprising a) 70 wt% - 98wt% of a high pressure low density polyethylene homopolymer, produced in a tubular reactor, having a melt index of 2 to 8 g/10 min according to ISO 1133 (190°C, 2.16 kg) and a density of 915 to 935 kg/m3 according to ISO 1183 and b) 2 wt% - 30 wt of a long chain branched, low-density polyethylene, having a melt index MFR of 2.5 to 10.0 g/10 min according to ISO 1133 (190°C, 2.16 kg), a density of 910 to 935 kg/m3 according to ISO 1183 and - a dynamic viscosity η0.05 at a shear rate of 0.05 rad/s and a dynamic viscosity η300 rad/s which satisfy the following relationship: η300≤108Pa*s+0.0253*η0.05 and/or - a phase shift δ0.5 at a frequency of 0.5 rad/s and a phase shift δ300 at a frequency of 300 rad/s, which satisfy the following relationship: tan δ300≥0.45+0.16*tan δ0.05 and its use.