We present results in a constraint solving approach for automatic generation of Inkjet print masks. Print masks are used to control the firing of the nozzles, that is, to determine which nozzles on an Inkjet printer cartridge are to spit an ink droplet at each particular instant in a multiple-pass print mode. Many design rules for print masks can be modeled in terms of constraints and cost functions. For example, if adjacent nozzles are fired simultaneously, printing artifacts often result. Therefore, spatial adjacency constraints with respect to horizontal, vertical and diagonal neighbors are modeled with various cost functions. Minimizing the associated, total costs then generates the print masks. Initial solutions are found by a greedy algorithm with some randomization; then neighborhood search techniques are applied to find local near-optima. Our approach can generate masks for Inkjet printers in multiple-pass print modes for multiple-level, multiple-drop echnologies. It has been used to help design the print masks for Hewlett Packard's wide format printers (DeskJet 2500C and 2500CM). This approach can shorten the turnaround time for print mask design in a systematic and methodical way.

A novel ink jet printing technology using ink mist jet has been developed. It enables multilevel printing within a single dot because a density controllable cluster of fine ink droplets is formed by focused ultrasonic waves. The ultrasonic wave radiated into an ink chamber is reflected by the parabolic chamber wall and focused on a nozzle hole. Under the suitable driving condition of the ultrasonic transducer, a traveling surface wave is generated at the ink meniscus and it separates many fine ink droplets at the peak point of the wave. Changing the number of ultrasonic waves within the interval to achieve one dot printing can control the density of the cluster. We have obtained a print sample with reduced graininess using a prototype print head employing a 10 MHz transducer that produces ink droplets with an average diameter of 2.5 μm. We also confirmed a basic performance having a maximum optical density of 2.3, 32 controllable gray levels and a resolution of 300 dpi using glossy paper with a dot frequency of 2 kHz.

Recent advances regarding the measurement and theory of equilibrium contact angles on real surfaces are reviewed. The intrinsic contact angle is discussed in terms of the Young equation and the line tension concept. The fundamental question that is presented and discussed is the relationship between the intrinsic, actual and apparent contact angles. Apparent contact angle measurement using the Capillary Bridge System (CBS) is explained. The main advantages of this approach are the use of force measurements rather than direct optical measurements, and the ability to calculate an average apparent contact angle. The Wenzel equation for rough surfaces and the Cassie equation for heterogeneous surfaces are shown to be true only for drops that are very large compared to the scale of roughness/heterogeneity. Contact angle hysteresis is explained. Of special interest is the predicted difference between the drop and captive bubble techniques, which stems from contact angle hysteresis.

We describe the development of microporous paper sheet that meets the demands for print quality in different types of digital printing. The paper sheet contains a microporous layer that has a surface pore diameter of 0.5 to 30 μm and a density of 0.2 to 0.5 g/cm³. The microporous layer can be easily obtained by coating a sheet substrate with a stirred resin-containing liquid, which forms bubbles. Applications for the microporous paper sheet in digital printing include thermal wax transfer (including resin type), thermal dye diffusion transfer, direct thermal, solid inkjet and toner-based marking. In the first application, the microporous layer acts as an ink-receiving layer (see Fig. 1) due to the heat-insulating nature, the compressibility and the surface structure. The microporous paper sheet has a thermal conductivity of 0.25 W/(m.K) or less. The compression stress of the microporous sheet under a high compression of 10% by volume is controlled to 8 kg/cm² or less. The molten ink permeates sufficiently into the region of the microporous surface layer due to the presence of a large number (3,000/mm² or more) of fine pores distributed on the surface. Thus the microporous surface layer enhances the print quality for use in thermal wax transfer printing. Print qualities of the microporous paper sheets are quantitatively analyzed using automated image analysis systems with test targets that consist of basic image elements such as dots, lines and solid areas. The print qualities ncluding dot raggedness, dot reproduction, line blurriness, line raggedness, tone reproduction, mottle, graininess and optical density of the microporous paper sheets are consistently higher than those observed for a plain paper sheet. For example, by measurement with the ISO-13660 draft standard, the lead line blurriness and raggedness of a microporous paper sheet are 27 μm and 1.8 μm, respectively, whereas those of a plain paper sheet are 57 μm and 7.4 μm, respectively.

Advances in ink jet printing technology have enabled the output of digital images that rival the quality of images produced on photographic film. As a result, there is demand for ink jet media with intermediate and high gloss finishes, so that the ink jet printed image resembles a photographic image. Coated ink jet media are necessary to produce the desired glossy image characteristics. Existing coating technologies can be divided into those that are resin rich, and those that are pigment rich. The latter coatings are microporous as a result of the packing of small, inorganic particles. A key ingredient used widely in both types of systems is amorphous silica, which imparts many desirable characteristics to the coating and final image. We report here novel submicron-sized materials, based on amorphous silica gels that can be used to prepare high capacity ink-receptive coatings that also exhibit gloss finishes. As a result of their internal porosity, the materials can be used to produce coatings with substantial void space for liquid absorption. As a result of their small particle size, the materials can be used to produce films of relatively high gloss, even in a pigment rich coating film. These new materials should play an integral role in the development of coated, glossy media for high productivity ink jet printers.

Fabric printing is a bottleneck in the textile-apparel supply pipeline. It is commonly believed that digital printing systems will replace the current methods of printing textiles. Xerography is one of the digital printing technologies being investigated for textile printing at the Georgia Institute of Technology. The research reported in this paper has focused on developing polymerbased xerographic toners giving required printed fabric properties. The suitability of toners produced through mechanical grinding processes for xerographic textile printing is discussed. Three classes of polymeric binders (amorphous polyester, three thermosets, and five polyamides) were studied. The potential of these binders was evaluated using crockfastness (rub fastness) and fabric flexural rigidity tests. Materials that could be ground to the required particle size were too rigid. Thus the printed fabrics had high flexural rigidities and, in many cases, unacceptable wet crockfastness ratings. The potential of a more flexible resin, which could not be ground to the required particle size, was assessed by applying toners via a solvent medium. The flexible resin gave the required textile properties.

Silsesquioxanes are a class of silicone polymers that are useful as abrasion resistant overcoats for organic photoreceptors. We have manipulated the electrical properties of this sol-gel matrix by incorporating a solid electrolyte. Solid electrolytes, also referred to as solid ionic conductors, are materials in which electrical conductivity is provided by the motion of ions. We chose (3-glycidoxypropyl)trimethoxysilane (GPS) as the most suitable commercially available monomer to form the polymer matrix for lithium iodide migration. This epoxysilane contains two ether oxygen atoms for coordination to low lattice energy salts. A good correlation was observed between the level of GPS and the electrical properties of the coating, with increasing concentration of GPS in the silsesquioxane resulting in decreased resistivity. The silsesquioxane is a hard material and the resistivity remained relatively high, between 10¹⁰–10¹³ ohm-cm. However, this is a desirable resistivity for maintaining image quality with an overcoated photoreceptor.

Non-polar electrical field flow fractionation (Np-EFFF) has been demonstrated to separate electrophotographic toner particles suspended in hydrocarbon medium according to the ratio of their diffusivities and their electrophoretic mobilities. While electrophoretic mobility has long been recognized as critical to the behavior of liquid toner particles in a development gap, the role of diffusivity has largely been ignored. Toner particles move in the development gap as a function of both parameters, and as toner particle size is reduced to achieve improvements in print quality, diffusivity becomes increasingly important. We present a method of quantifying and predicting the behavior of toner particles in the development gap of a print engine. Particles eluting from the Np-EFFF channel at the same retention volume would be expected to exhibit similar development characteristics in a printer. Consequently, Np-EFFF retention volume data can be used to predict image development performance of liquid toner particles. Using this instrument with the multi-angle laser light scattering (MALLS) detector permits simultaneous determination of particle size, and particle size distribution. Although it is theoretically possible to determine other fundamental particle parameters from Np-EFFF data, it is used here to separate particles for further analysis down steam. In practical application, these instrumental capabilities allow screening of very small toner test batches, thus conserving time, expense, and the amount of waste generated.