Health concerns as a result of harmful UV-rays drive the development of UV-sensors of different kinds. In this research, a UV-responsive smart textile is produced by inkjet printing and UV-LED curing of a specifically designed photochromic ink on PET fabric. This paper focuses on tuning and characterizing the colour performance of a photochromic dye embedded in a UV-curable ink resin. The influence of industrial fabrication parameters on the crosslinking density of the UV-resin and hence on the colour kinetics is investigated. A lower crosslinking density of the UV-resin increases the kinetic switching speed of the photochromic dye molecules upon isomerization. By introducing an extended kinetic model, which defines rate constants k_colouration, k_decay and k_{decolouration}, the colour performance of photochromic textiles can be predicted. Fabrication parameters present a flexible and fast alternative to polymer conjugation to control kinetics of photochromic dyes in a resin. In particular, industrial fabrication parameters during printing and curing of the photochromic ink are used to set the colour yield, colouration/decolouration rates and the durability, which are important characteristics towards the development of a UV-sensor for smart textile applications.

Photochromism is a light-induced reversible change in colour defined as: ‘A reversible transformation in a chemical species between two forms having different absorption spectra brought about by photo-irradiation.’ This issue of Textile Progress provides a review of photochromism, the different methods for producing photochromic textiles, their properties, the measurement of kinetic colour changes, and their application in photochromic textiles. Photochromism can be utilised in a variety of textile products from everyday clothing to high-technology applications such as protective textiles, medical textiles, geo-textiles and sports textiles. Although photochromic materials have been used since 1960 to cut down the transmission of light through the lenses in sunglasses, there has been limited further development since that time due to technical difficulties not only in the application of photochromic colourants, but also with the measurement of kinetic colour-changing properties. Renewed interest in photochromic textiles has arisen due to improved commercial potential in particular for applications as photochromic nanofibres, in ‘smart’ textiles and in ‘smart’ clothing.

The development and design of novel functional and smart textile materials such as textile sensors and multicolored systems based on photochromic dyes necessitate controls of color intensities, switching speeds, and material durability. Precise control and synchronization of dye kinetics are important for multi-colored photochromic applications especially. However, durability towards abrasion and washing should not be compromised on if we aim to design reliable future textile products. In this study, two different commercial photochromic dyes — a naphthopyran and a spirooxazine-based dye — have been applied on PET fabric by inkjet printing and UV-LED curing. The photochromic textiles’ color behavior, fastness to abrasion and washing, and handle are evaluated using spectrophotometry, scanning electron microscopy, and Kawabata evaluation system. Despite a decrease in color performance after washing, the photochromic inkjet print is effective and barely influences the textile structure. Reduced rigidity of the host matrix promoted higher color yields and faster dye kinetics, but also improved durability towards abrasion and washing. In order to synchronize kinetics of the different dye types for multi-colored applications, distinct curing conditions are preferable, which, however, result in varying print durability. In the design of multi-colored photochromic textiles, dye kinetics, and durability have to be balanced.