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Since the invention of thermal ink jet in 1978, Hewlett-Packard has introduced a series of products based on this technology that have evolved from low resolution monochrome all the way to medium/high resolution color and black and white printers. The first HP product, introduced in 1984, had a resolution of 96 dots per inch. The latest HP offering is the DeskJet 1200C with a 300 by 600 dots per inch resolution for black and white and 300 dpi for color. The 1200C also utilizes HP's resolution enhancement technology to provide high-quality text printing. Given this range of development, the question that arises is "how far can this technology be taken?" Certainly the capability of thermal ink jet to deliver excellent color quality at an affordable cost is hard to challenge. Expectations in this area are still very high and even better color print quality is anticipated in the future. Although lasers deliver superb black and white text quality, the color capability of thermal ink jet makes the technology extremely attractive. There are two ways to look into the future of thermal ink jet. One would be to analyze the engineering issues, along with the manufacturing challenges, that will determine the practical limits of the technology. This obviously involves a discussion of the product plans for the future. A second approach, to be taken in this summary paper, will be to look at the physical limits and contrast them with the current state of the technology. To do this, four sub-systems common to all printing technologies will be defmed. The first, ink storage and delivery, is directly dependent to the issues that affect the life of the pen and overall print speed. Secondary concerns in this area are user re-supply and serviceability. The second subsystem is that of transfer. The transfer process involves the separation of a defined amount of colorant and the mechanism whereby that colorant is deposited on the substrate. Fundamental questions in this area focus on ultimate dot size; i.e., resolution, and print speed. The third subsystem is that or addressing; i.e., receiving and electronically converting print data into the drive voltages for the thermal ink jet resistors. Limitations in addressing technology will have a direct bearing on the size of printhead swath for scanning printheads or the cost of a page-wide array. The final, and possibly most complex subsystem, is fixing of the image to the substrate. This brings into play all of the chemistry involved in ink and paper interactions and the demands for the devices to be able to print on a wide variety of substrates. This is a situation unlike any in commercial printing where inks are selected for the appropriate paper stock. Technology issues here will have a strong bearing on overall print quality with particular emphasis of thermal ink jet's ability to print color graphics and images. This paper will provide a brief summary of the issues involved in these four subsystems from the point of view ofthe physical limits that constrain them.
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