Microcellular TPU Foaming With Counter-Pressure Mold Venting
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Solution Overview
Problem
Conventional microcellular foaming processes struggle to produce low density thermoplastic polyurethane (TPU) foam due to bubble collapse and uneven cell growth, resulting in high density and large voids, which affects the homogeneity and rebound resilience of the foam, limiting its application in sports goods and shoe soles.
Innovation Solution
A microcellular foaming process involving the use of supercritical fluid, counter pressure gas, and a mold with venting holes to control cell growth, achieving low density and homogeneous foam by introducing a counter pressure gas into the mold before or during injection and releasing it after injection, with venting holes distributed across the mold to facilitate uniform cell expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional microcellular foaming process is used to produce TPU foam, then the foaming process is simple, but the bubbles collapse and cells do not grow uniformly, resulting in high density and large voids
Solution Approach 1:
The mold is segmented into multiple functional zones with venting holes distributed throughout the cavity. These venting holes create localized pressure relief zones that enable uniform cell nucleation and growth across different regions of the foam, preventing bubble collapse and achieving homogeneous low-density structure.
Solution Approach 2:
Counter pressure gas is introduced into the mold before or during the injection of the TPU mixture. This preliminary action establishes a controlled pressure environment that prevents premature bubble collapse and allows cells to grow uniformly throughout the foam matrix, achieving the desired low density and homogeneity.
2Manufacturing precision
If counter pressure gas is introduced and venting holes are added to the mold, then foam density is reduced and homogeneity is improved, but the mold structure becomes more complex
Solution Approach 1:
The mold incorporates a porous structure with venting holes distributed throughout the cavity. These pores allow controlled gas flow and pressure equalization during the foaming process, enabling uniform cell growth and achieving homogeneous foam structure while managing the complexity through a systematic pore distribution pattern.
3Manufacturing precision
If venting holes with diameter 0.05-1 mm and density 1-8 holes/cm³ are used, then cell growth is uniform and density is low, but the mold design becomes more complex
Solution Approach 1:
The venting holes are designed with specific parameter ranges: diameter of 0.05-1 mm and density of 1-8 holes/cm³. These parameter changes create optimal conditions for uniform cell nucleation and growth throughout the foam, achieving consistent low-density structure while the systematic parameter specification manages design complexity.
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 process produces TPU foam with a density of 0.3 g/cm³ or less and voids less than 2 mm, enhancing homogeneity and rebound resilience, making it suitable for sports goods, shoe soles, automotive parts, and leisure goods.
Implementation Method 1
a supercritical fluid (SCF), such as nitrogen or carbon dioxide, is dosed into a thermoplastic polymer melt in the machine barrel. It creates foaming structure in the article by gas expansion upon depressurization in the cavity of a mold.
Implementation Method 2
gas expansion upon depressurization in the cavity of a mold
Implementation Method 3
introducing counter pressure gas into a mold to build up a counter pressure
Data Source
Figure 1~2
Figure 3(a)~4(d)
AI summary
The invention relates to a process to produce low density thermoplastic polyurethane (TPU) foam via microcellular foaming process, which includes introducing a counter pressure gas into a mold to build up a counter pressure and the mold has venting holes distributed all over the mold. The present invention also relates to the low density TPU foam thus obtained and to the use of the foam in sports goods or shoe sole.