Coextruded Polyamide Cap Layer for Foam Shear Protection
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Solution Overview
Problem
The existing methods for producing vehicle interior trim components using low-pressure molding (LPM) face issues such as foam shear and degradation due to high injection temperatures, leading to defects like 'orange peel' and excessive waste, particularly when using bilaminates or trilaminates, which increase production costs and waste material.
Innovation Solution
A physically crosslinked, closed cell polyolefin foam with a polyamide cap layer is coextruded and laminated to a film, fabric, or foil, providing a protective barrier that remains intact at injection temperatures, reducing the need for additional offal and minimizing material waste, and allowing direct injection into the mold cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If polypropylene is injected at high temperature (200°C) to fill the mold, then the mold cavity is properly filled to form the panel, but the hot polypropylene shears away or degrades the foam since the injection temperature is well above the melting temperature of the foam
Solution Approach 1:
A polyamide barrier layer is introduced between the injected polypropylene and the foam layer. This intermediary layer has a melting temperature above the polypropylene injection temperature, allowing it to withstand the hot polypropylene without degrading while protecting the underlying foam from thermal damage and shear forces.
Solution Approach 2:
The patent changes the temperature parameter of the barrier layer by selecting a polyamide with a melting point higher than the injection temperature. This parameter change allows the barrier layer to remain solid and protective during the injection process, unlike the foam layer which would melt at these temperatures.
2Reliability
If the polypropylene injection temperature is reduced to protect the foam, then foam degradation is reduced, but the polypropylene may not properly fill the mold cavity
Solution Approach 1:
The polyamide barrier layer serves as a thermal buffer, allowing the polypropylene to be injected at its optimal high temperature for proper mold filling while the barrier protects the foam from excessive heat. This intermediary enables both requirements to be satisfied simultaneously.
3Reliability
If a TPO or TPE protective layer is laminated to the foam to prevent shear and degradation, then foam protection is improved, but the layer thickness must be substantial which increases material costs and requires an additional lamination step
Solution Approach 1:
The protective barrier function is merged into the foam structure itself by coextruding the polyamide layer during foam formation. This eliminates the need for a separate lamination step and reduces overall complexity while maintaining protection.
Solution Approach 2:
The patent creates a composite structure where polyamide and foam are coextruded in a single continuous process. This composite approach provides both structural integrity and protective functionality without requiring separate processing steps.
4Reliability
If injection is performed at the offal portion of the bilaminate to avoid foam shear, then foam degradation is reduced, but the offal must be longer which increases waste and production costs
Solution Approach 1:
The polyamide barrier layer enables direct injection into the mold cavity by protecting the foam from the hot polypropylene. This eliminates the need for extended offal sections, allowing injection to occur at the standard location without compromising foam integrity.
5Reliability
If a trilaminate structure is used with a protective TPO or TPE layer, then foam protection is improved, but the additional layer and lamination step increase material costs and production complexity
Solution Approach 1:
The protective barrier and foam structure are merged into a single coextruded component. The polyamide layer is formed simultaneously with the foam during the extrusion process, eliminating the need for separate lamination operations and reducing overall manufacturing cost.
Solution Approach 2:
The protective barrier function is maintained continuously through the coextrusion process, providing uninterrupted protection throughout the foam structure without requiring discrete lamination steps that would interrupt production flow.
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 polyamide cap layer effectively prevents foam degradation and shear, reducing waste and production costs, while maintaining the integrity of the foam structure, thus enhancing the manufacturing efficiency and quality of vehicle interior components.
Implementation Method 1
irradiating the coextruded layers with ionizing radiation
Implementation Method 2
a chemical foaming agent in an amount of 3-15 wt. %
Data Source
AI summary
Described herein are physically crosslinked, closed cell continuous multilayer foam structures that includes a foam layer comprising polypropylene, polyethylene, or a combination of polypropylene and polyethylene and a polyamide cap layer. The multilayer foam structure can be obtained by coextruding a multilayer structure comprising at least one foam composition layer and at least one cap composition layer, irradiating the coextruded structure with ionizing radiation, and continuously foaming the irradiated structure.