Multi-layer Elastic Articles with Pre-stretching
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Solution Overview
Problem
Existing methods for processing elastic polymers into films and fibers face challenges such as limited line speed due to tension-induced instability, tackiness leading to 'blocking' during storage, and poor aesthetics, including surface appearance and feel.
Innovation Solution
A multi-layer article comprising a low crystallinity layer and a high crystallinity layer, where the high crystallinity layer can undergo plastic deformation upon elongation, with the layers being pre-stretched to improve elastic and hysteresis properties, reducing permanent set and enhancing surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If elastic polymers are processed into films and fibers, then elasticity is achieved, but line speed is limited due to tension-induced instability
Solution Approach 1:
The elastic polymer is divided into multiple layers with different crystallinities (low crystallinity layer and high crystallinity layer). The high crystallinity layer provides dimensional stability and reduces tension-induced instability, enabling higher line speeds, while the low crystallinity layer maintains the desired elasticity. This segmentation allows the film to be stretched more uniformly at higher speeds without destabilizing elastic properties.
2Stability of the object's composition
If elastic polymers are processed into films, then elasticity is achieved, but tackiness causes blocking during storage
Solution Approach 1:
Different regions of the film have different properties: the high crystallinity layer provides a non-tacky, stable surface that prevents blocking during storage, while the low crystallinity layer maintains the bulk elasticity. This local differentiation allows the film to be elastic where needed while non-tacky where it contacts other surfaces during storage.
3Stability of the object's composition
If elastic polymers are processed into films, then elasticity is achieved, but surface appearance and feel are poor
Solution Approach 1:
The high crystallinity layer forms the surface with superior aesthetic properties including better surface appearance, reduced tackiness, and improved feel. The low crystallinity layer remains in the bulk to provide elasticity. This local quality differentiation resolves the contradiction by assigning surface aesthetics to the high crystallinity layer while preserving bulk elasticity in the low crystallinity layer.
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 pre-stretching process enhances the elastic and hysteresis properties of the articles, reducing permanent set and improving surface characteristics, thereby addressing the issues of line speed, tackiness, and aesthetics.
Implementation Method 1
the high crystallinity layer capable of undergoing plastic deformation upon elongation
Implementation Method 2
The article is elongated at a temperature below the melting point of the low crystallinity polymer in at least one direction to an elongation of at least about 50%
Implementation Method 3
enhances the elastic and hysteresis properties of the articles, reducing permanent set
Data Source
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Figure 3
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AI summary
In one embodiment the invention is an article comprising at least two layers, a first or low crystallinity layer comprising a low crystallinity polymer and a second or high crystallinity layer comprising a high crystallinity polymer. The high crystallinity polymer has a melting point as determined by differential scanning calorimetry (DSC) that is about the same or within less than 25C of the melting point of the low crystallinity polymer. The article is elongated at a temperature below the melting point of the low crystallinity polymer in at least one direction to an elongation of at least about 50% of its original length or width, to form a pre-stretched article. Preferably, the high crystallinity layer is capable of undergoing plastic deformation upon the elongation.