Supercritical CO₂ Dyeing and Foaming for Colored Expanded TPU
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Solution Overview
Problem
Conventional methods for coloring thermoplastic polyurethane (TPU) materials in sporting goods, such as sport shoes, are limited by the use of pigments which restrict color range and provide low rub-fastness, leading to staining issues and inefficiencies in the dyeing process.
Innovation Solution
A process involving the use of disperse dyes, acid dyes, or fluorescent whitening agents in supercritical carbon dioxide, combined with a foaming process, to create colored and expanded thermoplastic polyurethane (ETPU) materials, improving color depth and processing time while using environmentally friendly foaming gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If pigments are used for coloring TPU in conventional mass-dyeing process, then the coloring process is simple, but the color range is limited and rub-fastness is low causing staining
Solution Approach 1:
The patent changes the chemical parameters of the dyeing system by switching from pigment-based conventional dyeing to disperse dye or acid dye formulations specifically designed for supercritical fluid dyeing. This parameter change enables a broader color range and improved rub-fastness while maintaining process simplicity through the supercritical CO2 medium.
2Ease of manufacture
If pigments are used for coloring TPU, then the coloring process is straightforward, but rub-fastness is low leading to staining of mould
Solution Approach 1:
The invention changes the chemical composition parameters by using disperse dyes or acid dyes in supercritical CO2 instead of conventional pigments. This results in improved rub-fastness and eliminates staining issues while keeping the process straightforward through the supercritical fluid medium.
Solution Approach 2:
Supercritical carbon dioxide acts as an intermediary medium that enables the use of disperse dyes and acid dyes on TPU. This intermediary allows for better dye penetration and bonding to the polymer matrix, significantly improving rub-fastness and preventing staining of molds during subsequent processing.
3Device complexity
If conventional dyeing methods are used, then the process is simple, but color penetration depth is insufficient
Solution Approach 1:
Supercritical carbon dioxide serves as an intermediary carrier that penetrates deeply into the TPU matrix, enabling uniform color distribution throughout the material. The supercritical state allows the CO2 to diffuse effectively into the polymer structure, carrying the dye molecules to achieve deep and uniform penetration.
Solution Approach 2:
The patent utilizes phase transitions of carbon dioxide between supercritical and gaseous states to achieve deep color penetration. During the supercritical phase, CO2 penetrates the TPU matrix effectively; upon decompression to gaseous state, the CO2 expands and carries the dye throughout the material, ensuring uniform color distribution.
4Ease of manufacture
If traditional foaming gases are used, then the foaming process is conventional, but environmental contamination occurs
Solution Approach 1:
The patent uses supercritical carbon dioxide as an inert foaming agent that replaces conventional harmful foaming gases. CO2 is environmentally benign, non-toxic, and does not contribute to ozone depletion or global warming. The inert atmosphere ensures no environmental contamination while maintaining effective foaming properties.
Solution Approach 2:
The supercritical CO2 used as foaming agent can be easily recovered and reused after the foaming process. The CO2 is depressurized, allowing the foam structure to set, and the gaseous CO2 is then collected and recompressed for reuse, eliminating waste and environmental contamination while maintaining process efficiency.
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
This process allows for a wide range of color shades with improved rub-fastness and uniform color penetration, reducing contamination and increasing efficiency by using supercritical CO2, which does not pass into the effluent and can be reused, and enabling the use of disperse dyes and acid dyes without dispersants or diluents.
Implementation Method 1
placing the TPU material in an autoclave together with a colorant and/or a fluorescent whitening agent (FWA)... increasing the pressure in the autoclave by introducing the at least one gaseous fluid... allowing the non-expanded TPU material to saturate
Implementation Method 2
decreasing the pressure in the autoclave down to ambient pressure at a temperature between the melting temperature and the glass transition temperature (Tg) of the TPU material at such a rate that the TPU material expands (expansion step) to obtain coloured ETPU material
Data Source
AI summary
A process for the preparation of coloured and expanded thermoplastic polyurethane (coloured ETPU) material which comprises the following steps:a) providing thermoplastic polyurethane (TPU) material and at least one gaseous fluid wherein the melting temperature of the TPU material is above the supercritical temperature of the at least one gaseous fluidb) placing the TPU material in an autoclave together with a colorant and/or a fluorescent whitening agent (FWA), wherein the colorant is selected from at least one of a disperse dye, an acid dye and a pigment;c) increasing the pressure in the autoclave by introducing the at least one gaseous fluid at a temperature below the melting point of the TPU material and at least above the supercritical temperature of the at least one gaseous fluid at the applied pressure (saturation step); andd) allowing the non-expanded TPU material to saturate; ande) decreasing the pressure in the autoclave down to ambient pressure at a temperature between the melting temperature and the glass transition temperature (Tg) of the TPU material at such a rate that the TPU material expands (expansion step) to obtain coloured ETPU materialf) removing the coloured ETPU material from the autoclave.