Inkjet printer which deposits at least two fluids on a substrate such that the fluids react chemically to form a product thereon

A patterned product 8 is deposited directly onto a substrate 7 by a pair of inkjet printheads 1,2 which apply at least two fluids 3,4 which react chemically to form the product with properties differing from the fluids. The droplets may coincide during flight at 5 to form mixed droplets 6 which continue onwards towards the substrate. Alternatively, a pair of inkjet printheads may eject droplets (11,12,Fig.2) such that their point of coincidence (13) is at the substrate (14). The materials may also be deposited from multiple inkjet heads to prepare a wide range of reaction scenarios in the form of user-defined patterns which may be sequences of differing layers and possibly to build up thicker layers. A PCB may be printed by printing a metal salt and a reducing agent directly, instead of two colours from a conventional inkjet printer. To print a three-dimensional article, a pair of fluids which react to give a precipitate can be used instead. Repeated passes can then build up a desired shape. The two processes may be combined to produce composite devices such as electrical components. A wide variety of fluids may be used, for example fluids suitable for electroless deposition, or fluids selected such that the reaction yields a ceramic precipitate.