Process for dyeing and foaming thermoplastic polyurethane
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Solution Overview
Problem
Conventional methods for coloring thermoplastic polyurethane (TPU) materials are limited by the use of pigments, which restrict color range and provide low rub-fastness, leading to staining issues and limited options for decorative and safety applications, especially in demanding products like sport shoes.
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 achieve colored and expanded thermoplastic polyurethane (ETPU) with improved processing time and color depth, 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 replacing conventional pigment-based mass-dyeing with supercritical fluid extraction using CO2. This allows the use of disperse dyes and acid dyes that were previously incompatible with TPU, expanding the color range while maintaining processability. The supercritical state of CO2 enables unique solvation properties that facilitate better dye penetration and fixation.
Solution Approach 2:
The patent replaces the conventional mechanical mixing and heating-based dyeing system with a supercritical fluid extraction system. Instead of relying on mechanical agitation and high-temperature processing, the invention uses the solvating power of supercritical CO2 to transport and deposit dyes uniformly throughout the TPU matrix, achieving superior color fastness and broader color selection.
2Ease of manufacture
If pigments are used for coloring TPU, then the process is straightforward, but rub-fastness is low leading to staining of mould
Solution Approach 1:
The invention changes the physical and chemical parameters of the dyeing environment by using supercritical CO2 instead of conventional aqueous or organic carriers. This enables the use of disperse dyes and acid dyes that form stronger bonds with TPU, significantly improving rub-fastness. The supercritical state allows for controlled deposition and better integration of dye molecules within the polymer matrix.
Solution Approach 2:
Supercritical CO2 acts as an intermediary carrier that transports disperse dyes and acid dyes into the TPU material. The CO2 dissolves the dye compounds and delivers them uniformly throughout the polymer, facilitating deep penetration and strong bonding. After dyeing, the CO2 is removed by depressurization, leaving the dye firmly embedded in the TPU structure.
3Ease of manufacture
If conventional dyeing methods are used, then processing is simple, but color penetration depth is insufficient
Solution Approach 1:
The patent replaces conventional mechanical dyeing methods with supercritical fluid extraction. The supercritical CO2 penetrates deeply into the TPU matrix due to its gas-like diffusivity and liquid-like density, carrying dye molecules to the core of the material. This eliminates the surface-level coloring limitation of conventional methods and achieves uniform color distribution throughout the entire product thickness.
Solution Approach 2:
The invention utilizes the unique properties of supercritical fluids, which combine gas-like penetrability with liquid-like solvating power. The supercritical CO2 flows through the TPU material like a gas, accessing deep interior regions, while simultaneously dissolving and depositing dye molecules with the effectiveness of a liquid. This dual character enables superior color penetration and uniformity.
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 enables a wide range of color shades with improved rub-fastness and uniform color penetration, eliminating staining issues and allowing for the production of high-quality, vibration and shock-absorptive materials suitable for footwear.
Implementation Method 1
dyeing and foaming of thermoplastic polyurethane (TPU) material in supercritical fluids (such as supercritical carbon dioxide)
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)
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 fluid; b) 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); and d) allowing the non-expanded TPU material to saturate; and e) 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; f) removing the coloured ETPU material from the autoclave.