Uniaxially-Oriented LLDPE Films for Hygiene Backsheet Downgauging
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Solution Overview
Problem
Conventional non-breathable backsheets for hygiene products are thick and lack the ability to be downgauged without compromising film properties such as modulus, puncture force, and tensile strength.
Innovation Solution
Development of uniaxially-oriented ethylene-based polymeric films with at least 65 wt.% linear low density polyethylene, exhibiting specific properties like Comonomer Distribution Breadth Index, melt index, density, and crystallization elution fractionation, which are then stretched in the machine direction to form a composite laminated with a nonwoven for use in hygiene articles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional cast film process is used to manufacture non-breathable backsheets, then sufficient film stiffness and barrier properties are achieved, but the film thickness must be increased which adversely affects downgauging goals
Solution Approach 1:
The patent changes the molecular parameters of the LLDPE resin by controlling comonomer distribution breadth (CDBI ≥ 60%), melt index (1.8-10 g/10min), density (0.910-0.940 g/cc), and molecular weight distribution (Mw/Mn < 3.0). These parameter changes enable the resin to form highly oriented crystalline structures upon uniaxial stretching, achieving high film stiffness at reduced thickness
Solution Approach 2:
The patent creates a composite structure through uniaxial orientation that aligns polymer chains in the machine direction, forming a composite-like microstructure with enhanced mechanical properties. The resulting film exhibits anisotropic properties with high stiffness in the orientation direction while maintaining thin gauge
2Quantity of substance
If film thickness is reduced for downgauging, then material usage and weight are decreased, but film properties such as puncture force and tensile strength deteriorate
Solution Approach 1:
The patent utilizes specific LLDPE resin parameters (CDBI ≥ 60%, Mw/Mn < 3.0) that enable efficient chain packing and crystallization upon stretching. This results in high strength-to-thickness ratio, maintaining puncture force and tensile strength even as material quantity is reduced through downgauging
Solution Approach 2:
The patent transitions from isotropic thin film structure to anisotropic uniaxially-oriented structure. By introducing directional orientation through machine direction stretching at controlled draw ratios (2.5-5.0) and temperatures (20-50°C below peak melting temperature), the film gains enhanced mechanical strength in the orientation direction, compensating for reduced thickness
3Length of stationary object
If uniaxial stretching is performed at high draw ratio to achieve thin gauge, then film thickness is reduced, but manufacturing precision and film property uniformity may be compromised
Solution Approach 1:
The patent specifies precise processing parameters: draw ratio of 2.5-5.0 and draw temperature of 20-50°C below peak melting temperature. These controlled parameter changes ensure uniform stretching and crystallization throughout the film, maintaining property uniformity even at high draw ratios that produce thin gauge
Solution Approach 2:
The patent performs preliminary orientation of polymer chains through controlled uniaxial stretching before final film formation. This preliminary action at optimized temperature and draw ratio ensures uniform molecular alignment and crystalline structure development, preventing defects and property variations in the final thin film
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 solution allows for the creation of thinner, high-performance non-breathable backsheets that maintain desired film properties, enabling downgauging while ensuring effective barrier and tensile properties.
Implementation Method 1
stretching is performed at a draw ratio of 2.5 to 5 at a draw temperature, Td, of 20°C to 50°C less than the peak melting temperature, Tm, of the linear low density polyethylene
Implementation Method 2
the LLDPE has a crystallization elution fractionation (CEF) fraction at 70°C to 90 °C of equal to or greater than 80% of the total CEF Fractions
Data Source
AI summary
A uniaxially-oriented ethylene-based polymeric film having at least one layer comprising at least 65 wt.%, based on total amount of materials present in the at least one layer, of a linear low density polyethylene which exhibits each of the following properties: a CDBI of at least 60%; a melt index, I2, measured according to ASTM D 1238 (2.16 kg @190°C), of 1.8 g/10 min to 10 g/10 min; a density of from 0.910 g/cc to 0.940 g/cc; and a Mw/Mn of less than 3.0.