A new process known as liquid additive manufacturing (LAM) is making it possible to print useful components onto textiles with polyurethane.

Additive manufacturing or 3D printing is now widely employed for adding components onto textiles in applications such as smart textiles, filter media and fuel cell membranes, but to date these parts have been applied via the photocuring of polymers or silicone. Wevo-Chemie, based in Ostfildern-Kemnat, Germany, has developed tailor-made reactive resins that improve both the processing conditions and the durability of  such components when using the LAM process.

3D printing offers greater freedom in design and enables the existing functions of textiles and textile components to be optimised and additional functions to be incorporated. Polyurethane reactive resins also provide a number of additional advantages over the materials that have been predominantly used so far.

In the LAM process, two reactive components are usually blended in a mixing and metering unit and printed directly onto the textile. This can be done without supporting structures, such as those used, for example, in stereolithography (SLA) – the oldest additive manufacturing process. Wevo’s LAM products achieve the material properties necessary for the process by adding thixotropic additives to adjust the stability and the catalysts used to fine-tune the reaction times.

In addition, no light source is needed to cure Wevo reactive resins, because the blend of resin and hardener components leads to the chemical reaction starting as soon as the mixture is dispensed by the print head. The exact curing time of the products – usually just a few minutes – can be individually adjusted by adding catalysts. The process time can be further shortened by using infrared (IR) heaters.

The chemical structures in polyurethanes are very similar to those in polyamide, polyester, polyacrylonitrile and elastane fibres, which results in the formation of hydrogen bonds which ensure significantly better bonding of the material to the synthetic fibres compared to silicones. In addition, polyurethane wets the fibres well without penetrating them, making the textiles highly durable.

The choice of polyol components employed in the resin formulation of Wevo’s products and their combination with the right hardener components for a specific application also allows the mechanical properties of a product to be adjusted anywhere between very soft and elastic and very hard. This results in very good chemical resistance, for example to disinfectants and surfactants, such as those used in dry cleaning. A further modification of the materials enhances the hydrophobic, water-repellent properties of the textiles – for low water absorption and consequently improved washability.

A wide range of other functions offered by these Wevo products can be tailored to individual requirements. They include, for example, flame-retardant properties for the manufacture of protective clothing, as well as a thermoregulating effect through the addition of phase-change materials (PCMs) or thermally conductive fillers. It is also possible to adjust electrically conductive and/or antistatic properties in smart textiles such as  sensor applications or textile heating fabrics, such as seat heaters in cars.

A multitude of potential applications can be implemented with the  Wevo products, from designer and decorative elements to structural reinforcements or the application of logos and lettering. It’s also possible to incorporate electrical and electronic components such as sensors or antennas using conductive adhesives and inks. The resins can additionally be used to encapsulate peripheral devices such as sensors, LEDs, batteries, power supply units or circuit boards in smart textiles. And in the field of membrane technology, the reactive resins can be used to seal and bond fibre mats, such as in the manufacture of nonwovens, enabling them to be used in filtration technology or in fuel cell components.

www.wevo-chemie.com