LLDPE-LDPE Blend for Extrusion Coating Neck-In Control
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Solution Overview
Problem
Low density polyethylene (LDPE) extrusion compositions lack sufficient abuse resistance and toughness, while linear low density polyethylene (LLDPE) and ultra low density polyethylene (ULDPE) compositions exhibit unacceptably high neck-in and draw instability, limiting their extrusion processability and maximum operating speed in coating applications.
Innovation Solution
A blend of linear low density polyethylene (LLDPE) with high pressure low density polyethylene (LDPE) is used, where LLDPE constitutes 50-97% by weight, with specific characteristics such as density, melt index, and comonomer distribution, to achieve low neck-in and excellent draw stability, allowing for higher haul-off rates without breaking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If LLDPE is used to improve abuse resistance and toughness, then physical properties are improved, but neck-in increases and extrusion processability deteriorates
Solution Approach 1:
The patent applies parameter changes by carefully controlling the molecular weight distribution (Mw/Mn < 2.8), comonomer distribution constant (45-400), and vinyl unsaturation (<0.12 vinyls per 1000 carbon atoms) of the LLDPE component. These specific parameter ranges optimize the balance between toughness and neck-in behavior, allowing improved physical properties while maintaining acceptable extrusion processability
Solution Approach 2:
The patent creates a composite extrusion composition blending LLDPE (50-97% by weight) with HDPE or other polyethylene resins. This composite approach combines the toughness benefits of LLDPE with the processability advantages of HDPE, achieving a synergistic effect that resolves the contradiction between improved strength and reduced neck-in
2Manufacturing precision
If LDPE is used to achieve low neck-in and good extrusion processability, then manufacturing precision is improved, but abuse resistance and toughness deteriorate
Solution Approach 1:
The patent merges LLDPE and HDPE into a single extrusion composition, combining their complementary properties. The LLDPE provides toughness and abuse resistance, while the HDPE contributes to low neck-in and good extrusion processability. This merging allows both requirements to be satisfied simultaneously in the final composite material
Solution Approach 2:
The patent develops a composite material system where LLDPE (50-97% by weight) is blended with HDPE or other polyethylene resins (3-50% by weight). This composite structure enables the material to exhibit both the toughness characteristics of LLDPE and the low neck-in properties of HDPE, resolving the contradiction between strength and manufacturing precision
3Strength
If high molecular weight LDPE is used to improve abuse properties, then strength is improved, but melt strength becomes too high for successful drawdown at high line speeds
Solution Approach 1:
The patent applies parameter changes by controlling the melt index of the LLDPE component (I2 in the range of 4.0 to 25 g/10 min) and the overall composition (I2 in the range of 4 to 20 g/10 min). These parameter specifications ensure the melt has appropriate flow characteristics for high-speed drawdown while maintaining sufficient abuse resistance in the final product
Solution Approach 2:
The patent applies local quality by having different molecular weight components serve different functions: the LLDPE fraction (with controlled Mw/Mn < 2.8) provides toughness and abuse resistance, while the HDPE fraction provides processability and appropriate melt strength. This functional differentiation within the composite allows simultaneous achievement of high strength and high productivity
Data Source
AI summary
A composition of matter suitable for use in extrusion coating applications is disclosed. The composition comprises a blend of particular LLDPE with particular LDPE. The LLDPE has the following characteristics: a density in the range of from 0.89 g/cc to 0.97 g/cc; an MWD less than 2.8; a melt index (I2) in the range of 4.0 to 25 g/10 min; a Comonomer Distribution Constant in the range of from greater than from 45 to 400; and a vinyl unsaturation of less than 0.12 vinyls per one thousand carbon atoms present in the backbone of the ethylene - based polymer composition. The LDPE has a melt index (I2) in the range of 0.1 to 15 g/10 min, and has a melt strength which satisfies the inequality: Log Melt strength (cN} > 1.14 - 0,6 X Log l 2 (g/10 min, 190°C).