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

The patent is about a method for coloring polymer substrates, such as fibers, using a dye called a colorant. The method provides greater depth of color at lower temperatures than traditional methods, making it more energy efficient and cost-effective. The method can be used on sensitive fibers and can also be applied to different types of colorant. The method involves adding a second solvent system to the colorant solution, which lowers the solubility of the colorant and allows for uptake into the substrate. The second solvent system can be added in a predetermined amount or continuously over a period of time. The method can lead to 100% uptake of the colorant and leaves no colorant behind in the substrate. Overall, the patent presents a novel and effective way to color polymer substrates with various types of colorant.

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.

Where polyesters are combined (either woven together as a blend or joined together as parts of a garment) with these materials, other less effective dyeing methods must be used (which can lead to discernible differential colour strengths for the individual fabrics in the blend) or pre-dyed fabric must be blended, which is a complex and costly process.

This carrier facilitates the dyeing of the fabric and allows the use of lower temperatures than HT dyeing, typically 98° C. However, the carriers often have detectable smells, they often impair the light fastness of the dyed material and they also pose environmental concerns and, as a result, HT dyeing processes predominate commercially nowadays and the use of carrier dyeing has steadily declined.

However, organic solvents are ineffective for disperse dyeing because the dye has a greater affinity for the solvent than it does for the fibres.

Consequently, when disperse dyes are applied from organic solvents low dye uptake onto the fibres is achieved so that the depth of shade that can be accessed using high temperature aqueous dyeing techniques cannot be replicated using organic solvent based dyeing liquors.

The methods can also be time consuming.

For example, dyeing with vat dyes is a complicated, time-consuming, multi-stage process that involves several pH changes and requires the use of environmentally questionable strong reducing agents.

Although many strategies have been explored for treating dyeing effluent that contains residual dyeing auxiliaries, no single treatment method is effective for all auxiliaries or types of dye / fibre system.

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