HDPE-Core Multilayer Films for Ultrasonic Nonwoven Bonding
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Solution Overview
Problem
Ultrasonic bonding of nonwoven substrates with polypropylene films often results in poor adhesion and pinholes, compromising the barrier functionality of cloth-like backsheets used in hygiene products.
Innovation Solution
A multilayer film structure comprising a core layer of high density polyethylene with specific density and melt index, sandwiched between skin layers containing a combination of polypropylene and low density polyethylene, enhances adhesion and reduces pinholes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ultrasonic bonding is used to join polyethylene film to polypropylene nonwoven substrate, then productivity is improved, but adhesion deteriorates resulting in poor bond quality
Solution Approach 1:
The patent applies composite materials by creating a multilayer film structure where a polyethylene core layer is bonded to polypropylene skin layers, which in turn are ultrasonically bonded to a polypropylene nonwoven substrate. This composite structure allows the polypropylene skin layers to act as an intermediate material that is compatible with both the polyethylene core and the polypropylene substrate, thereby achieving strong adhesion while maintaining high productivity through ultrasonic bonding.
Solution Approach 2:
The polypropylene skin layers serve as an intermediary between the polyethylene core layer and the polypropylene nonwoven substrate. This intermediate layer resolves the adhesion problem by providing a material that is chemically compatible and bondable with both sides, enabling effective stress transfer during ultrasonic bonding without direct contact between incompatible polyethylene and polypropylene surfaces.
2Adaptability or versatility
If different materials are used for nonwoven substrate and film to achieve functional requirements, then adaptability is improved, but adhesion deteriorates resulting in poor bond quality
Solution Approach 1:
The patent applies local quality by assigning different material properties to different layers of the film structure. The core layer uses polyethylene for specific functional requirements (such as flexibility or barrier properties), while the skin layers use polypropylene to provide local adhesion quality that matches the nonwoven substrate. This spatial differentiation of material properties allows the structure to meet both functional requirements and adhesion requirements simultaneously.
3Productivity
If ultrasonic bonding is used to join dissimilar materials, then productivity is improved, but pinholes are generated destroying barrier functionality
Solution Approach 1:
The multilayer composite structure with polypropylene skin layers provides a more uniform bonding interface during ultrasonic bonding, preventing the formation of pinholes that would compromise the barrier functionality of the core layer. The composite structure distributes the bonding stress more evenly across the interface.
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 multilayer film structure provides improved adhesion to nonwoven polypropylene substrates, reduces pinholes, and maintains softness and low noise characteristics, suitable for producing high-quality cloth-like backsheets.
Implementation Method 1
a nonwoven substrate at least partially ultrasonically bonded to the multilayer film to form a laminate
Data Source
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AI summary
A multilayer film comprising a core layer and two skin layers, wherein the core layer is positioned between the two skin layers, wherein the core layer comprises a polyethylene composition comprising a high density polyethylene having a density of 0.930-0.965 g/cc and a melt index of 0.7-10.0 g/10 min, and wherein each skin layer independently comprises a polypropylene composition comprising greater than 50 wt.%, based on the total weight of the polypropylene composition, of a propylene-based polymer.