The finishing of textiles goes digital!

For several years, digital printing, especially digital inkjet printing, has been one of the technologies in the textile industry with strongly increasing demand in the field of textile coloration. Only about 30 % of the textiles are printed and from this third only a small percentage is printed digitally today. However, the predicted growth rates for digital textile printing are high, ranging from 8-10 %/year. Furthermore, about 90 % of the textiles produced are treated with chemicals to achieve a certain functionality or to give the textile a desired property. Due to the variety of available chemicals, the functionalization possibilities of textiles are very different today. All these functionalities require a formulation especially adapted to the substrate for a reliable proof of function. The formulations are mainly applied to the textiles by analogous processes, such as padding.

Depending on the material absorption of the textiles, significantly more material is absorbed than is actually required for the function. This results in high energy consumption due to drying as well as high material consumption. Due to increasing ecological requirements, an innovative and sustainable technical approach is needed. This approach should also meet the requirements of the market that is facing a high product diversification.

Zschimmer & Schwarz Mohsdorf is a manufacturer of textile auxiliaries and is developing digitally printable finishing chemicals as part of the project. Suchy Textilmaschinenbau is a manufacturer of textile machinery and has a fundamental knowledge of special machinery construction of finishing machines for the textile industry. Textilausrüstung Pfand is a contract textile finisher specializing in the finishing of a wide variety of textile substrates with different functionalities and extremely small quantities/running meters. druckprozess is a provider of digital inkjet printing machines for industrial applications. The expertise is the development of new business models for this technology.

STFI

Digital printed optical brightener on cotton fabric

As a research institution, the STFI is developing the processes for applying the chemicals. Within the digiTex-Pro project, it is responsible for the laboratory-scale tests and advises the project partners with testing and validation the generated samples. The project partners form a consortium that results in a coop-erative collaboration on all parameters (chemistry, machine, process, application) that make sense for the process. After a comprehensive market survey of the technical possibilities, various potential digital printing technologies were tested. This resulted in the final selection of a printing technology that allows a wide range of chemicals to be processed.

A first machine demonstrator was presented at the International Textile Machinery Exhibition ITMA 2019 in Barcelona/Spain. With this equipment, it is already possible to apply a quantity of chemicals of up to 60 g/m2, whereby the desired quantity of material can be varied. At the moment the speed can be up to 30 m/min (single-pass). This enables similar results to be achieved in terms of coating quantity and speed as with analog processes (e.g. padding). Another advantage of this digital application technology is the comparatively simple and fast change of chemicals. The time-consuming cleaning of chemical bath sand the disposal of chemical waste are no longer necessary. The machine technology allows quick and easy cleaning with a suitable cleaning agent. This helps to increase the productivity of the process. In addition to full-surface application of the chemistry, the digital application technology also enables near-net-shape partial chemical application, i.e. application of the chemistry in patterns. This reduces the amount of unnecessarily finished material, which is removed in further processing steps.

STFI

Textile digitally treated with chemistry formulations to obtain hydrophobic and hydrophilic properties at different area on one and the same textile (hydrophobic/hydrophilic areas are made visible by pure water droplets, the water form droplets with high contact angle on hydrophobic areas whereas the water is penetrating into to textile at hydrophilic areas).

Material consumption can be calculated in advance on the basis of the digital print data, thus enabling a transparent work process and economical use of functional chemicals. In addition, the application technology used is a non-contact printing process. Therefore, even very sensitive substrates or textiles with a 3-dimensional surface can be homogeneously finished. It is also possible to combine several functionalities next to each other and on top of each other on the textile substrates. This aspect will be investigated more intensively during the remainder of the project. So far, selected functional chemicals for hydrophilization, hydrophobization and optical brightening have been developed into printable ink formulations and successfully applied to various textile substrates.

Similarly, tests were carried out with other functional formulations. These included an antiviral and an anti-odor formulation. The advantages of the machine concept are especially the flexibility of the digital printing technology. This allowed, for example, the partial material application of a hydrophobic coating.

Also, the application proved to be advantageous with regard to the ongoing corona pandemic. Within a short time, mask materials could be finished with an additional hydrophobic protective layer. The material could be applied to the prefabricated materials without contact. Since this is a digital finishing process and the ink formulations are applied in droplet form, the required quantities of the functional substances can be varied as desired depending on the textile material and structure and also on the position on one and the same textile. This allows the droplet size to be adjusted as required so only the outer surface is functionalized (top) or the textile is completely penetrated (bottom).

STFI

Cross-sectional image of a digitally finished textile (the applied functional chemical is made visible by blue color)

The parameters are to be adjusted to the textile substrates and can be stored in a database. This enables easier machine operation with regard to returning or similar products. The sustainability of the new digital finishing process shows great potential. Waste volumes can be reduced by 80-90 % per batch. The consumption of chemicals is reduced, and the curing time can also be reduced due to the low material application. This saves energy as well as waste water, as the cleaning effort of the system in case of an upcoming material change is significantly reduced compared to conventional finishing processes.

Acknowledgements
The research project “digiTEX-PRO" is still an ongoing research project funded by the German FederalMinistry of Education and Research (BMBF) as part of the program "Twenty20 Partnership for Innovation" (futureTEX).
For further information, please visit: www.futuretex2020.de

Tobias Petzold
Saxon Textile Research Institute e.V. (STFI)
Chemnitz/Germany