Compression Molded Foam Articles Retaining Microcellular Structure
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Solution Overview
Problem
The challenge in producing compression molded polymeric foam articles is the tendency of the heat and pressure applied during the molding process to crush the cell structure of the foam, making it difficult to maintain a quality cell structure.
Innovation Solution
A method involving the extrusion of a polymeric material with a blowing agent to form a pellet with an average cell size of less than 150 microns, which is then compressed between mold halves, using a nozzle configuration that promotes cell nucleation and growth, and limiting the compression piston stroke to retain small cell size and density reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If heat and pressure are applied during compression molding to shape the foam, then the molding process can be completed, but the cell structure of the foam is crushed
Solution Approach 1:
The foam precursor is pre-formed with the desired cell structure through extrusion before compression molding. This preliminary formation of the foam structure allows the subsequent compression molding to shape the article without destroying the cell structure, as the foam is already configured properly before the high heat and pressure application
Solution Approach 2:
The patent controls and optimizes the parameters of heat and pressure application during compression molding. By carefully adjusting these parameters, the process achieves adequate shaping while minimizing cell structure damage, resolving the contradiction between completing the molding process and preserving cell quality
2Loss of substance
If the average cell size is reduced to less than 150 microns, then material savings increase, but the compression molding process becomes more difficult
Solution Approach 1:
The microcellular foam structure with average cell size less than 150 microns is created during the extrusion of the precursor, before compression molding. This preliminary creation of the fine cell structure allows the material to achieve high material savings while avoiding the difficulty of creating such fine cells during the compression molding process itself
Solution Approach 2:
The process separates the foam formation step from the shaping step. The extrusion process creates the segmented cellular structure with small cell sizes, while the compression molding process focuses on shaping the article. This segmentation of functions allows achieving both small cell sizes and ease of manufacture
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 retains small cell sizes and density reduction throughout the compression molding process, resulting in articles with excellent mechanical properties and material savings, suitable for various applications including closures.
Implementation Method 1
conveying a stream of polymeric material and blowing agent in an extruder
Implementation Method 2
The mold cavity is closed with heat and pressure being applied to shape the precursor into the desired molded polymeric article
Implementation Method 3
compressing the mold portions to form a compression molded foam article
Data Source
AI summary
Compression molded polymeric foam articles and methods are described herein. Equipment design and processing techniques may be controlled to form compression molded articles having desired characteristics.