Stretchable Sheet Neck-In Suppression via Ultrasonic Bonding
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Solution Overview
Problem
Existing methods for manufacturing stretchable sheets, such as those used in absorbent articles, face issues like neck-in, which leads to uneven stretching stress and increased material costs due to the need for wider elastic films and difficulties in achieving uniform air permeability.
Innovation Solution
A method involving a heat melting apparatus with an anvil roll and ultrasonic horn, where the elastic film is stretched between a counter roll and an anvil roll with a speed difference, and bonded to sheet layers with strategically placed protrusions to suppress neck-in and create through holes for air permeability, reducing material costs and ensuring uniform stretching stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an elastic film is stretched in the machine direction to impart elasticity, then elasticity is achieved, but neck-in occurs causing width reduction and increased material costs
Solution Approach 1:
The elastic film is divided into multiple narrow films arranged side by side, with spaces between them. This segmentation prevents the continuous film from contracting uniformly (neck-in) during stretching, as each narrow film can be independently positioned and secured, maintaining overall width while achieving elasticity.
Solution Approach 2:
A porous intermediate layer is introduced between the elastic film and the outer sheet layers. This intermediary layer allows the elastic film to stretch and contract freely while maintaining positional stability, preventing neck-in by distributing the mechanical stress and providing a compliant substrate that accommodates the elastic deformation.
2Strength
If an elastic film is stretched in the machine direction, then elasticity is achieved, but uniform stretching stress cannot be obtained due to neck-in
Solution Approach 1:
By segmenting the elastic film into multiple narrow parallel films, the contraction force is distributed across discrete segments rather than a continuous mass. This segmentation ensures uniform stress distribution across the width of the laminate, as each segment can be independently positioned and the gaps between segments prevent concentrated contraction forces.
3Strength
If a stretchable sheet structure is made impermeable to provide elasticity, then elasticity is achieved, but air permeability is reduced causing stuffiness
Solution Approach 1:
The intermediate layer is designed with porous structure, allowing air and moisture vapor to pass through while providing mechanical support. This porous intermediary layer maintains breathability and comfort by enabling air circulation, while still allowing the elastic film to function properly for providing elasticity and stretchability.
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 method effectively suppresses neck-in, reduces material costs, and ensures uniform stretching stress and air permeability in the stretchable sheet, enhancing its performance in absorbent articles like disposable diapers.
Implementation Method 1
bonding is performed by a heat melting apparatus comprising an ultrasonic horn for bonding and an anvil roll
Implementation Method 2
the elastic film passes along the counter roll and then passes along the anvil roll, wherein the elastic film is stretched by making a circumferential speed of the anvil roll faster than a circumferential speed of the counter roll
Data Source
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AI summary
To provide a method for manufacturing a stretchable sheet capable of suppressing neck-in. In a supplying step, a stretchable elastic film 30 is interposed in a stretched state between a first sheet layer 21 having no elasticity and a second sheet layer 22 having no elasticity. In the supplying step, heat melt energy is applied to a region of a large number of bonded portions spaced apart from each other by a heat melting apparatus from the outside of the first sheet layer 21 and the second sheet layer 22 to melt the elastic film 30. The first sheet layer 21 and the second sheet layer 22 are bonded directly or via an elastic film at the large number of bonded portions. The elastic film 30 is caused to pass through the counter roll 63 and the nip roll 65 to pass along the counter roll 63 and then pass along the anvil roll 60, and the elastic film 30 is stretched by making the circumferential speed of the anvil roll 60 faster than the circumferential speed of the counter roll 63.