The textile jigger carries out wet chemical processes such as dyeing and bleaching, most typically on synthetic polymer fabrics. Jiggers work by unrolling a length of fabric through a heated impregnation liquid made up of reactive dyes or bleach in accordance with set formulae.
The industrial jigger has benefited from a number of improvements in recent years, including increased programming and automation and the improved control of dyebath composition. Nevertheless, the basic principles of jigger operation have not changed and the procedure remains lengthy and often poorly regulated. The treated fabric spends relatively little time in contact with the hot liquid before moving on to an uptake roller where temperature is not controlled. The inevitable cooling which occurs reduces the effectiveness of the process.

Breaking with tradition

This project, launched in September1994, proposed the introduction of microwave irradiation, which was complementary to traditional heating techniques, to maintain optimum temperatures throughout jigger operations. The project followed upon an Electricité De France (EDF)-supported study which demonstrated that such a system was not only capable of cutting treatment time, but also of improving dye yields irrespective of the type of material treated. The principle of using electromagnetic waves in a textile jigger was subsequently patented by EDF and the Institut Textile de France (ITF).
The specific aim of this project was the production of an industrial-scale system for textile preparation and dyeing using microwave assistance. This pilot system was to be fitted with control instrumentation to allow for the accurate measurement of energy consumed and the evaluation of ecological performance. Comparisons were made with traditional methods using the same machine, with particular attention being paid to final product quality.

Prototype success

A prototype machine was created based on a LAJTOS industrial jigger. Machine operation was managed by an automated system, allowing predetermined injection of dyes and auxiliaries, fabric unwinding, and management of microwave power and safety systems. A heating coil immersed in the liquid served as the main source of heat. Additional heating was provided by microwave generators located on top of the machine and operating at up to 30 kW of power. Microwave radiation was distributed over the length of the fabric being processed.
The most significant results were obtained in the treatment of cotton, where improvements were observed on all of the major efficiency measures. Dyeing efficiency was increased by 10%, chemical pollution was reduced by 5%, salt consumption went down by 25% and finishing time was reduced by about 7%.

Material benefits for cotton

Project partners emphasise that while the results for cotton treatment were highly significant and clearly demonstrated the economic viability of the new system, the improvements achieved in the treatment of synthetic polymers, already a more efficient process than for cotton, probably do not in themselves justify its installation - the cost of the equipment is simply too high when compared with the benefits obtained. If, on the other hand, cotton is being treated, then the system offers clear economic benefits.
The use of heat-generating microwaves is a radical development in terms of the mechanism of reactive dye transfer. Partners say the new process will mean enormous cost savings and increased productivity for European textile producers, many of which are SMEs. Furthermore, the system is extremely environmentally friendly and represents a real improvement in terms of working conditions. Environmental benefits include energy savings, a reduction of the quantity of chemicals used, and reduced water and salt consumption.

Market potential

Increasing demands for faster delivery of smaller lots and a larger diversity of products have had profound effects on the textile-finishing sector, making the use of automated processes such as jigging even more attractive and, indeed, necessary. The use of microwave technology to maintain optimum temperature conditions represents an important advance for European textile finishers at a time when textile manufacturing is moving away from Europe towards countries with lower labour costs. Market research has identified at least 150 jiggers in Europe which could benefit substantially by using the new system in the treatment of cotton.