Low temperature colouring method

Abstract

The present invention relates to a method of colouring polymer substrates at low temperatures. The method comprises subjecting the polymer substrate that is to be coloured to a colouring liquor comprising a solvent in which the colourant has a high solubility and then adding a solvent in which the colourant has a low solubility, typically water.

Description

[0001]The present invention relates to a method of colouring polymer substrates at low temperatures. The method comprises subjecting the polymer substrate that is to be coloured to a colouring liquor comprising a solvent in which the colourant has a high solubility and then adding a solvent in which the colourant has a low solubility, typically water. The method is particularly useful for dyeing polyester fibres and polyester fibre blends with disperse dyes.BACKGROUND[0002]A large proportion of the textile products produced in the world today comprise polyesters. In particular poly(ethylene terephthalate) (PES) accounted for ˜58.5% (53.1×106 T) of the 90.6×106 T world textile fibre demand in 2015. The outstanding success and enduring popularity of PES fibres can be attributed to their generally excellent textile characteristics and high chemical resistance, coupled with the ability of polyester fibre to be manufactured in virtually any physical form as required for different applica...

AI Technical Summary

Benefits of technology

[0018]The polymer substrate may be a fibre substrate. The colourant may be a dye. The inventors have found that greater depth of colour can be achieved using the same quantity of colourant when using the above method than can be achieved using HT disperse dyeing methods. This greater depth of colour is achieved at a lower temperature than used in conventional HT methods and it is not necessary to use dispersing agents. Thus, the method of the first aspect is likely to be less energy intensive, less costly and pose lower risk to the environment than known HT methods. Also being a low temperature process it can be performed on or in the presence of sensitive natural and man-made fibres. Without wishing to be bound by theory, it is believed that the addition of the second solvent system to the solution of the colourant in the first solvent system lowers the solubility of the colourant in the solvents. This in turn gen

Problems solved by technology

Commercial disperse dyes typically comprise up to 60% by mass dispersing agent, adding considerably to the cost of the dyes.

Dispersing agents (examples include lignin sulfonates or formaldehyde polycondensates or arylsulfonic acids) are not particularly environmentally friendly.

The removal and disposal of such materials from the dyed textile fibre at the end of dyeing adds considerably to the cost, energy efficiency and environmental risk of commercial dyeing.

Currently, the vast majority of polyester fibre is dyed using such immersion processes at 130-140° C. Because such high temperatures are required for dyeing, the dyeing process is energy-intensive and the machines that are utilised for dyeing must be able to operate at pressures >1 atmosphere; consequently, the machines are typically very expensive.

Such compounds migrate to the fibre surface during HT dyeing and can deposit on the surfaces of both the fibre and machine during cooling, which can reduce the visual depth of shade brilliance of dyeings; the removal of the compounds from the dyeing machine constitutes an additional problem in immersion dyeing.

This process adds additional time to the process as well as additional materials and energy.

It also generates environmentally unacceptable efluents, including Na2S2O4 and, in the case of azo-disperse dyes, aromatic amines biproducts.

A further limitation of HT dyeing methods is that many fabrics, and particularly natural fabrics (e.g. wool, silk) and more sensitive manmade fabrics (e.g. polyurethanes, for example, Lycra®) are not stable under the high temperature conditions.

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