Polyester dyeing made simple

BASF's dyexact XP is a new application package designed to make the batchwise dyeing of polyester easier says James Carnahan

With synthetic and polyester fibres now dominating the world fibre market, the demand for the batchwise dyeing of polyester is increasing. To meet this demand, and to provide the dyer with the maximum accurate control over the entire process, BASF has developed dyexact XP, a new, integrated polyester dyeing system, which enables precise control of the dyeing process.

The essential core product of dyexact XP range, Basojet XP, has been designed to cater for all 100 per cent polyester exhaust dyeing, of which 70-80 per cent can be processed with this product alone, in combination with normal pH control. The concept is also aligned to the approach of "blind dyeing", allowing the dyer to control the inputs to the process and the process itself. Examples of these variable inputs can be water, fibre and dyestuff quality, a carry-over of processing chemicals into the dyebath, and the chemicals themselves, the process output is assured by the addition of specifically formulated dyexact XP components.

Productivity levels

In addition to the aspect of process control, BASF has targeted maximum productivity levels as critical. With the current fibre-growth projections of polyester on the rise, especially in the area of batchwise processing, extra demand will be placed on existing systems for additional capacity. According to BASF, levels of investment can be minimized through maximizing existing productivity levels, something made possible with dyexact XP.

"The range itself must be designed in such a way as to be cost effective to the dyer", explained BASF "Thus BASF is offering a range of products from which a selection will be made according to the prevailing conditions within the dyehouse. In the way, the company can choose the system most suited to cost-effective solutions to those problem areas that exist, rather than an overall solution, which could be superfluous and therefore cost ineffective. This range of products includes:

Basojet XP: A "core" recommendation for the dyeing of polyester, which has been formulated to be able to dye polyester within "normal conditions within certain specified parameter tolerances.

• An XP-'support' range, which would only be used when certain specific parameters are outside 'normal' tolerances.

According to BASF, Basojet XP, the basis of dyexact XP range, is an effective leveling and disposing agent with excellent anti-oligomer property suitable for high temperature dyeing of polyester with disperse dyes. It offers a large number economic and ecological advantages such as pro-control and high levels of process reliability.

"Due to the inherent properties of Basojet, research has shown that between 70-80 per cent of all batchwise processed polyester could be processed using only this product at the recommended pH level, without the need for further additives", says BASF.

Support Product Range

In addition to the Basojet XP, BASF points out there are occasions where additional control is necessary for those parameters that are outside the "normal" tolerance. According to BASF, these parameters are: leveling, dispersing, chelating/sequestering, lubricating, fastness, oligomer contamination, scouring and softening.

For the scouring support product, BASF has created Kieralon XP-S. During the dyeing process, it is important that the substrate is free from contamination of products that may have a negative influence on the dyeing process itself. Scouring prior to dyeing is normally done to remove fibre processing aids and other contaminants. Some products are self-emulsifiable. but BASF advised that even these should be removed, as often the emulsions are not stable under dyeing conditions.

Kieralon XP-S, specifically designed for batchwise processing, conforms to these requirements and, in addition, says BASF, has an excellent wetting property that assists in the loading of the machine, reducing time and fabric entanglements. The product is non-foaming and can be applied in neutral to alkaline conditions.

For leveling, there is Palegal XP-L. In some instances the dyestuff selection for the shade is not always optimal in terms of compatibility or levelness performance on all polyester fibres. The use of Palegal XP-L, in conjunction with Basojet XP, significantly increases this leveling and migration performance. This allows the dyer to achieve a higher degree of levelness on the substrate using recipes consisting of dyestuffs that have been chosen specifically for their performance in other criteria.

For dispersing, BASF has produced Setamol XP-D. The ability of the dyestuff to create and maintain a fine dispersion throughout the dyeing process is critical to the mechanism of disperse dyeing. Transition of the disperse dyestuff into its water soluble state is necessary for fibre penetration, and the particulate size of the dispersion will affect this rate of transition. Setamol XP-D and Basojet XP are stable to high temperatures and this ensures that the dispersion is maintained throughout the dyeing process. Setamol XP-D would only be used in those cases where the inherent properties of the dyestuffs exhibited extremely poor dispersion characteristics.

With certain machine/substrate combinations, effective lubrication is necessary to prevent running problems during processing. Primasol JET remains the BASF primary offer in this area. The nonionic character also indicates that it has no influence on other processing chemicals and therefore can be used in all stages of the process. It has key performance in lubricity, liquor retention and crush/crease prevention.

The quality of water, in particular hardness, can have a significant effect on disperse dyeing. It is important to use a sequestering agent that is stable to high temperatures and is effective within the pH range of the dyeing process. Trilon XP-C demonstrates these abilities and is also bio-eliminable.

For oligomer control, BASF has produced Uniperol XP-O. Oligomer deposition on the substrate and machine can cause considerable problems in the dyeing of polyester. The production of oligomer is dependent upon the quantity of low-molecular polyester produced during the polyester synthesis. The use of Basojet XP will keep these small quantities of oligomer in a fine dispersion, thus allowing them to be discharged during the drain at the end of the dyeing process.

With polyester dyeing, achieving the right colour fastness is crucial. The level of fastness is dependent upon the fibre type and quality, the selection of disperse dyes used in the dyeing process and subsequent heat processes used in the finishing of the substrate. In order to reduce these poor levels of fastness, BASF says that Cyclanon ECO is an effective reducing agent that can be employed directly into the dyebath under acidic conditions at the end of the dyeing process. This had a number of significant cost and processing advantages in the reduction of process time, reduction in energy consumption, water savings and increased processing reliability.

Source: The Society of Dyers and Colourists

(The author is Strategic Marketing Textiles, Performance Chemicals, BASF Aktiengesellschaft, Ludwigshafen, Germany)