Inkjet printed indicators

Abstract

Inkjet is an exceptionally versatile printing technology, which application areas vary from inexpensive desktop printers for home printing to photo-quality wide format printers for graphic arts applications and ultra-high-speed digital printing machines for transactional and book printing. Because inkjet is a digital method – where liquid drops are generated from a print head driven by computer controlled electronic signals – very small amounts of material can be added and aligned precisely. Inkjet is also the only non-contact printing method, because there is no interaction between the print head and printing substrate during printing. This means that topography of printing substrate or shape of a printed object isn't as critical as it is in other printing methods, which often require relatively planar, smooth and durable printing surfaces. These two features make the inkjet technology especially appealing also for manufacturing applications. VTT has worked with inkjet technology more than a decade in the areas of publication and packaging production. In the end of last decade, we got interested in developing manufacturing methods based on inkjet. One of our goals has been the development of inkjet printed quality indicators.Optical indicators are based on active compounds, which undergo a definite colour chance depending on changes in exposure conditions. Indicators are used to monitor, for example, food product quality in real time and also remaining shelf-life can this way be better estimated. VTT has developed and patented special ultra-low-cost ink jet printable indicator systems for example in checking the freshness of food supplies. VTT has also developed indicator monitoring systems based on emerging camera phone technology. In this paper, the technologies and the operational environment, in which the new camera phone based indicator applications are developed, are described.