Polyethylene Cast Films for Diaper Backsheet Downgauging
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Solution Overview
Problem
There is a challenge in downgauging non-breathable diaper backsheet films made from Ziegler-Natta HDPE and LLDPE resins without compromising film stiffness, toughness, and line speed during manufacturing.
Innovation Solution
Development of cast films with a polyethylene composition characterized by specific properties, including a melt index, density, melt flow ratio, molecular weight distribution, and vinyl unsaturation, formed using a multi-metallic procatalyst in solution polymerization, which enhances the balance of stiffness and toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If Ziegler-Natta HDPE and LLDPE resins are used to make non-breathable backsheet films, then the films can be manufactured with good processability, but further downgauging significantly compromises film stiffness, toughness, and line speed
Solution Approach 1:
The patent applies parameter changes by precisely controlling multiple polymer composition parameters including melt index (1-20 g/10 min), density (0.935-0.970 g/cm³), melt flow ratio (5.5-7.0), molecular weight distribution (2.2-3.5), and vinyl unsaturation (>0.12 vinyls per 1000 carbon atoms). This multi-parameter optimization enables downgauging while maintaining film stiffness and toughness that single-parameter adjustments cannot achieve
Solution Approach 2:
The patent creates a composite polymer composition by reacting ethylene with alpha-olefin comonomers to produce an interpolymer with specific properties. This composite material structure combines the benefits of different monomers to achieve both downgauging capability and mechanical strength, rather than using homopolymers or simple blends
2Weight of moving object
If film thickness is reduced to downgauge the backsheet, then material usage and weight are reduced, but film stiffness and toughness are compromised
Solution Approach 1:
The patent uses parameter changes to decouple film weight from strength properties. By optimizing molecular weight distribution (2.2-3.5) and vinyl unsaturation (>0.12 per 1000 carbons), thinner films maintain adequate toughness and stiffness. The controlled melt index (1-20) ensures proper flow and filling at reduced thickness without sacrificing mechanical performance
3Productivity
If higher line speed is used during manufacturing, then productivity is improved, but film quality and process control become more difficult to maintain
Solution Approach 1:
The patent applies parameter changes to the polymer's melt characteristics, specifically controlling melt index (1-20 g/10 min) and melt flow ratio (5.5-7.0). These parameters are optimized to provide appropriate melt strength and flow characteristics that enable stable processing at higher line speeds while maintaining consistent film quality and reducing defects
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 new cast films allow for further downgauging while maintaining or improving stiffness, toughness, and line speed, making them suitable for hygiene and medical applications.
Implementation Method 1
formed using a multi-metallic procatalyst in solution polymerization
Data Source
AI summary
Disclosed herein is a cast film comprising a polyethylene composition comprising the reaction product of ethylene and optionally one or more alpha-olefin comonomers, wherein said polyethylene composition is characterized by the following properties: a melt index, I2, measured according to ASTM D1238 (2.16 kg, 190° C.), of from 1 to 20 g/10 min; a density (measured according to ASTM D792) of from 0.935 to 0.970 g/cm3; a melt flow ratio, I10/I2, wherein I10 is measured according to ASTM D1238 (10 kg, 190° C.) of from 5.5 to 7.0; a molecular weight distribution (Mw/Mn) of from 2.2 to 3.5; and a vinyl unsaturation of greater than 0.12 vinyls per one thousand carbon atoms present in the backbone of the composition.