Rapid development of inkjet printing technologies in the last 20 years resulted in making this technique widely available in office printers. At the same time, a number of benefits has been noticed in this approach of applying substances on surfaces in industrial applications. Precision and easiness of control of fluid application allows to limit manufacturing wastes and obtain products impossible to be created with classic coating techniques.
Electrically conducting path printed using ink-jet technology (SEM image). Visible non-uniformity of width influences conduction quality
Adaptation of the ink-jet technology for digitally controlled manufacturing of functional fabrics is the central point of the project. In particular, the works were focused on designing of materials reacting on environmental factors such as: temperature changes, humidity changes, electromagnetic fields, biocontamination, and others. The reaction of the functional fabric to an external stimulus may be e.g.: colour change, release of accumulated substance or change of electric properties.
Three main work areas were distinguished within the project:
Designing fabric functionality.
Among desired functions of materials resulting from using active substances were protective functions (flame resistance, antistatic properties, bactericide properties), monitoring (change of properties such as colour, electric parameters upon contact with an external stimulus) and active (controlled release of encapsulated substance, e.g. drugs).
The role of SKA Polska in these works was to perform research on parameters of inks and fabrics influencing the printing process (thus, key parameters for the process of functional fabrics design) and to design measurement methods for most important of these parameters (e. g.: wetting angle of a single fibre against the functional fluid).
Technology of functional substances deposition
The following technologies have been considered as possible for adapting for the project: Drop-On-Demand (DoD, the most commonly present in office printers), Continuous Ink Jet (CIJ, a technology widespread in the industry, used, among others, for printing dates on food products) and JetStream. Adaptation of these technologies required deepening of knowledge related to the process of digital printing and construction of mathematical models describing processes occurring during the printing.
SKA Polska took part in designing and manufacturing a prototype of a system enabling synchronization and appropriate positioning of a print on a fabric in the case of several subsequent processes.
Printing process monitoring
Print heads available for printing using an InkJet printing technology are adjusted, first and foremost, to colour inks and thus – to a defined range of physcial parameters of the liquid, such as density or viscosity. Properties of functional fluids may not fit into this range, or may be found at its border causing the printing process to become unstable, resulting for example, with gradual or complete clogging of printing nozzles. Because printed substances are often invisible, one cannot control the state of the head by observing the fabric being printed . Thus, a system monitoring the printing head itself is necessary, in order for the control system to detect each potential drop of quality of the printed fabric, and so the head may be automatically cleaned when necessary.
SKA Polska has developed and tested the optical, online monitoring system for the printing head. Besides detecting single clogged nozzles, thanks to use of advanced algorithms of data processing, the system may also estimate size and speed of generated droplets , and thus predict, when particular nozzles may stop functioning.
28 companies and scientific institutes participated in the project, including the renown Belgian textile institute and known universities from England, Belgium and the Netherlands, as well as two research units and three companies from Poland.