Low Density Ethylene Polymer Composition for Bubble Stability
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Solution Overview
Problem
Blown film production lines are limited by bubble stability, and existing ethylene-based polymer compositions fail to achieve an optimized balance of melt strength, optical, mechanical, and processing properties, particularly when using LDPE/LLDPE blends, which often result in poor film quality and increased production costs.
Innovation Solution
A composition comprising a first ethylene-based polymer with specific Mw(abs) and MS versus I2 relationships, and a second ethylene-based polymer with controlled melt index, density, and branching, produced through a high-pressure free-radical polymerization process in a tubular reactor, optimizing melt strength and processability while minimizing ultra-high molecular weight fractions that cause gel formation and reduce optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LDPE with very broad MWD and ultra high molecular weight fraction is used to increase melt strength, then bubble stability and film output are improved, but gel formation occurs and optical performance deteriorates
Solution Approach 1:
The patent extracts and removes the ultra high molecular weight fraction (>10^6 g/mol) from the LDPE molecular weight distribution through controlled polymerization conditions. This eliminates the gel-forming component while retaining the beneficial broad MWD characteristics that provide high melt strength and bubble stability.
Solution Approach 2:
The patent changes the polymerization parameters including operating at lower conversion levels (10-30%), controlling temperature gradients, and adjusting residence time distribution in the reactor system. These parameter changes produce LDPE with broad MWD but without the ultra high molecular weight fraction that causes gels.
2Ease of operation
If LDPE with very broad MWD is used to achieve high melt strength, then processing performance is improved, but optical performance of films is reduced
Solution Approach 1:
The patent optimizes polymerization parameters including temperature profiles, pressure conditions, and catalyst deactivation rates to produce LDPE with broad MWD up to Mw/Mn ≥ 4.0 while controlling the upper molecular weight limit. This achieves the desired processing performance while minimizing optical degradation.
3Strength
If autoclave based reactor systems are used to produce broad MWD LDPE, then high melt strength is achieved, but production costs increase and ultra high molecular weight fraction is formed
Solution Approach 1:
Instead of using traditional autoclave reactors that produce ultra high molecular weight fractions, the patent inverts the approach by using tubular or loop reactors with controlled residence time and conversion levels. This alternative methodology achieves broad MWD and high melt strength without the associated cost penalties and gel formation problems.
Solution Approach 2:
The patent changes the reactor operation parameters including maintaining lower conversion levels (10-30%), controlling temperature gradients along the reactor, and adjusting monomer feed rates. These parameter changes enable cost-effective production of broad MWD LDPE without ultra high molecular weight fractions.
4Reliability
If LDPE content in blend is increased to improve melt strength, then bubble stability is enhanced, but film performance contribution from LLDPE is reduced
Solution Approach 1:
The patent changes the molecular weight distribution parameters of the LDPE component to achieve maximum melt strength at lower LDPE concentrations. By controlling Mw/Mn ratio and eliminating ultra high molecular weight fractions, the patent enables effective blends with reduced LDPE content, thereby maintaining bubble stability while preserving LLDPE's film-forming properties and productivity.
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 composition enhances bubble stability, increases film output by up to 15% at maximum output rate, improves mechanical and optical properties, and reduces production costs by allowing higher LDPE content without compromising processing performance, leading to films with superior mechanical and shrink performance.
Implementation Method 1
A composition comprising: a) a first ethylene-based polymer, formed by a high pressure, free-radical polymerization process
Data Source
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AI summary
The invention provides a composition comprising the following: A) a first ethylene-based polymer, formed by a high pressure, free-radical polymerization process, and comprising the following properties: a) a Mw(abs) versus I2 relationship: Mw(abs) < A x [(I2)B], where A = 5.00 x 102 (kg/mole)/(dg/min)B, and B = -0.40; and b) a MS versus I2 relationship: MS ≥ C x [(I2)D], where C = 13.5 cN/(dg/min)D, and D = -0.55, c) a melt index (I2) from greater than 0.9 to 2.5 g/10 min; and B) a second ethylene-based polymer; and wherein the second ethylene-based polymer has a melt index (I2) from 0.1 to 4.0 g/10 min.