Inkjet Printing of Highly Loaded Particulate Suspensions
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Inkjet Printing of Highly Loaded Particulate Suspensions
Brian Derby and Nuno Reis Abstract Inkjet printing is an attractive method for patterning and fabricating objects directly from design or image files without the need for masks, patterns, or dies. In order to achieve this with metals or ceramics, it is often necessary to print them as highly concentrated suspensions of powders in liquids. Such liquid suspensions must have physical properties appropriate to the inkjet delivery mechanism. These properties are presented using a nondimensional formalism to illustrate the requirements for both drop formation and spreading on impact. Further critical issues relevant to inkjet printing of particulate suspensions are discussed and illustrated with experiments on a model alumina-containing colloidal suspension. Keywords: ceramic processing, fluid behavior, freeform fabrication, inkjet printing, particulate suspensions, rheology.
Introduction Inkjet printing was originally developed in the 1970s as a contactless printing method. Inkjet printing is now a ubiquitous technology and is routinely used for personal printing, commercial printing, and product marking. In the broadest sense, inkjet printing is a method of generating droplets of precise volume and selectively depositing these droplets. This concept has led to a series of applications in the fields of microdosing and precision fluid dispensing, rapid prototyping, and rapid manufacturing. In this article, we will explore the use of inkjet printing as a method for the manufacture of small components with electrical and mechanical applications. Inkjet printing deposits material in the form of a liquid. Therefore, in order to use inkjet printing to fabricate metal or ceramic parts, it is necessary to deliver the metal or ceramic materials in a liquid precursor form. The simplest way to achieve this is to disperse the required material as a fine powder suspended in a suitable liquid vehicle. The preparation and manipula-
MRS BULLETIN/NOVEMBER 2003
tion of powder-filled slurries is an important part of conventional powder processing technologies that have been applied to both ceramics and metals for many hundreds of years—for example, dissolving clay in water to form pottery slip, and depositing suspensions of oxides and metals as glazes and enamels. However, the required rheological properties of slurries usable for inkjet printing differ considerably from those used in many conventional forms of powder processing (e.g., screen printing or powder injection molding). Inkjet printing has been explored for a number of years as a tool for ceramic fabrication. Initial work by Sachs et al.1 did not directly print powder suspensions but instead printed a solution of binder materials onto a flat bed of metal or ceramic powder. This technique selectively bonds the powder patterned by the printed binder phase. A three-dimensional architecture is obtained by depositing subsequent powder layers followed by further printing. On completion of the process, all unbonded powder is
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