Extensible Web Laminate Necking Reduction via Two-Stage Stretching
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Solution Overview
Problem
Elastic films used in personal care articles face challenges such as necking, which leads to reduced elasticity, increased film width variability, and processing difficulties, resulting in waste and inefficiencies during manufacturing.
Innovation Solution
A method involving a multilayer film with two skin layers and an elastomeric core layer, activated in the cross-machine direction and then stretched beyond the deformation limit in the machine direction, followed by lamination with a web layer and recovery to produce an extensible web laminate, reducing necking and improving handling and waste reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If elastic films are stretched in the machine direction during processing, then the film can be laminated to web layers, but the film exhibits necking that reduces elasticity and increases width variability
Solution Approach 1:
The patent applies preliminary cross-machine direction stretching and activation to the multilayer film before the main machine direction stretching and lamination process. This preliminary action modifies the film structure in advance to reduce subsequent necking during MD stretching, thereby maintaining better width consistency while still enabling lamination.
Solution Approach 2:
The patent uses a composite multilayer film structure with skin layers and an elastomeric core layer. This composite structure allows the film to exhibit controlled mechanical properties, where the combination of layers provides both the necessary stretchability for processing and reduced necking behavior compared to single-layer films.
2Manufacturing precision
If the gap distance between sequential differential speed rolls is shortened to minimize necking, then film width variability is reduced, but greater stress on the elastic film results in more web breaks and process down time
Solution Approach 1:
The film undergoes preliminary cross-machine direction stretching and activation before machine direction stretching. This preliminary structural modification reduces the film's susceptibility to necking, allowing the use of larger roll gaps during MD stretching without significant width variability, thereby reducing stress and web breaks.
Solution Approach 2:
The patent changes the processing parameters by implementing a two-stage stretching approach with CD stretching first, followed by MD stretching. This parameter change allows for more favorable MD stretching conditions (larger gaps, lower stress) while achieving the same or better width consistency.
3Adaptability or versatility
If a nonwoven layer is bonded to the elastic film in the stretched state, then the laminate becomes extensible, but the elastic film width is confined by the nonwoven layer preventing relaxation to original width
Solution Approach 1:
The patent performs preliminary cross-machine direction stretching and activation before the final machine direction stretching and lamination. This preliminary action creates a modified film structure that maintains better dimensional stability during stretching, allowing the film to retain more of its elasticity after lamination while still providing the desired extensibility.
Solution Approach 2:
The composite multilayer structure with skin layers and elastomeric core provides a balance between extensibility and elasticity retention. The specific composition and structure of the composite film allow it to stretch appropriately for lamination while maintaining better recovery properties compared to single-layer films.
4Ease of operation
If intrinsically stretchable films are used in the machine direction, then the film can be easily processed, but the film is difficult to maintain under constant tension and is prone to premature stretching
Solution Approach 1:
The composite multilayer film structure provides controlled mechanical properties that balance ease of processing with tension stability. The combination of skin layers and elastomeric core creates a film that is stretchable when needed but maintains better dimensional stability and tension control during processing compared to intrinsically stretchable single-layer films.
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
This approach minimizes necking, enhances the efficient use of elastic material, reduces film waste, and improves processing capabilities by maintaining consistent film width and elasticity, leading to more efficient production of personal care articles.
Implementation Method 1
activating the multilayer film in a first direction, subsequently stretching the multilayer film past the deformation limit of the skin layers in a second direction perpendicular to the first direction
Implementation Method 2
recovering the multilayer film to produce an extensible web laminate
Data Source
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AI summary
A method of making extensible web laminates comprising a multilayer film and at least one web layer and the use of such extensible web laminates in personal care articles. The method generally includes activating the multilayer film in a first direction by stretching at least a portion of the multilayer film past the elastic deformation limit of the skin layers and recovering the skin layers with the elastomeric core layer to produce a multilayer film that is elastic in the first direction. The activated multilayer film is subsequently stretched beyond the deformation limit of the skin layers in a second direction substantially perpendicular to the first direction. At least one web layer is applied to the multilayer film while in the stretched state. The multilayer film is then recovered to produce an extensible web laminate.