Digital Finishing in the Textile Industry
What is digital finishing?
Digital finishing involves using a digital printer to apply a finish to textiles. This finish is a treatment that is not visible to the naked eye but provides the textile with specific functionalities such as flame retardancy, antimicrobial properties, UV stability, water repellency, and more. High-end textiles often undergo this treatment to enhance their performance.
The use of digital printers for applying finishes to textiles is a relatively new approach that offers significant advantages. One of the benefits is the reduction in the use of chemicals, as digital printers can precisely add chemicals at a very small scale (picolitre level). Moreover, digital printers have the capability to print patterns on only one side of the fabric, unlike traditional finishing methods that treat fabrics inside-out. This allows for precise and localized application of finishes.
With digital printing, it is possible to apply an antimicrobial finish only where it is necessary, such as on the front of garments and solely on the exterior of the fabric. This targeted application ensures efficient use of resources and maximizes the desired functionality of the textile.
This strategy aims to decrease the reliance on chemicals, water, and energy, while simultaneously ensuring the safety of individuals and the environment by minimizing their exposure to hazardous substances.
Why use digital finishes?
Digital finishing provides numerous advantages compared to traditional finishing techniques like padding or dipping. Unlike traditional methods that require a large bath containing all textile treating chemicals, digital printing allows for precise application of finishes only where they are necessary. This eliminates the need for immersing the entire fabric, resulting in less chemical waste and subsequent cleaning.
For instance, certain functionalities like water repellency may only be required on one side of a textile. Instead of applying it to the inside of clothing where it is unnecessary, digital printing enables targeted application on the outside. Moreover, digital printing is not limited to adding colors in various patterns and prints. It also allows for the incorporation of 'invisible' additives such as flame retardants, antimicrobial effects, UV protection, and water repellency.
This versatility expands the possibilities of digital finishing. Considering that many of these substances are harmful to the environment, it is more environmentally friendly to limit their usage to where they are truly needed. Digital finishing offers a more sustainable approach in this regard.
Is digital printing suited for all types of textile finishes?
No. The digital printing technique is not without its limitations. The small nozzles and valves of digital printers can result in technological drawbacks like the presence of large particles, agglomeration, and high volumes. Moreover, when compared to other manufacturing techniques, this method may be slower. Nevertheless, significant progress has been made in recent years. Numerous "pigment inks" have been introduced to the market. These binders are capable of carrying colorants or other additives and are compatible with various substrates, eliminating the need for a specific substrate.
Consider the following points:
There are many types of digital printers, but for the textile industry, piezo-head and valve-jet printers are the most common options.
The piezo-head printer has small nozzles and additional parts, making it the preferred technique for digital textile printing.
Printheads come in two types, with and without recirculation. Recirculation is needed when working with particles that tend to sediment (sink to the bottom) or cream (rise to the surface). A recirculating printhead ensures that pigments stay mixed and do not clog any parts of the printhead.
Printheads only work with certain types of binders. Some binders cannot pass the necessary filter tests for print heads. However, various commercially available binders for digital printers are available.
When additives are used, further developments are needed to ensure the ink has the correct viscosity, conductivity, and behavior.
Valve-jet printers are more tolerant of inks. Their nozzles are larger and the viscosity can therefore be higher. However, this technique does not give the same resolution when higher volumes are used. Although this is a limitation for some applications, it can be an advantage for others, such as thick substrates like carpets or non-woven textiles.
A case-study in the RELIANCE project
The Reliance project shows how textiles can become more environmentally friendly. It creates a new kind of antimicrobial particles that will be investigated in three cases (textiles, household appliances and automotive). In the textile application, a digital finish will be developed with these particles using high performance (partially) bio-based polyurethanes.
The project partners will provide a next-generation antimicrobial copper-doped mesoporous silica nanoparticle (Cu-SMIN) that will be ground into a dispersion for use in these bio-based polyurethanes. Then, it will be blended with the bioPU in suitable amounts and applied to Alsico High Tech's protective garments by digital finishing.
