HP Scitex FB6100 Printing Technologies - Page 18

Porous Coatings Porous coatings are opaque and usually made with an ink-receptive layer containing clay, calcium carbonate, or silica. For example, porous coatings are used in HP technical graphics papers and HP Heavyweight Coated Paper. These coatings quickly absorb the ink vehicle to produce fast-drying51 prints with sharp lines and crisp text. Porous coatings are designed to hold the colorant (both dyes and pigments) at or close to the surface of the print for high black optical density and excellent color saturation. They can provide the smooth, bright, white surface that is ideal for technical and presentation graphics. Nanoporous Coatings HP "Instant-dry" media52 use nanoporous coatings to produce prints that are dry to the touch out of the printer. These media offer good water-resistance, especially for dye-based inks.53 A nanoporous coating is composed of several layers over a photobase paper. Photobase paper forms the core of the print and provides a bright, white background for color imaging. This paper gives the print its thickness, weight, and stiffness. An outer, ink-permeable protection layer provides scratch and fingerprint resistance and can produce photographic prints with very high gloss. Ink vehicle and dyes pass through the protection layer to be absorbed by the imaging layer, where ink fills the voids in an open-matrix of pores between microscopic polymer particles. If the void capacity of the imaging layer is exceeded by printing with too much ink,54 liquid ink could be left on the surface ruining the print and possibly requiring printer maintenance. A resin coating provides a smooth substrate for the imaging and protection layers. It reduces curl after printing by blocking ink (and water) from entering the photobase paper. Dyes are trapped in the pores of the imaging layer. This gives dye-based inks on nanoporous media good water-resistance. But because the surface is permeable, atmospheric gases can diffuse into the imaging layer to react with dyes. Dye-based inks on nanoporous media generally have lower display permanence compared to the same inks on swellable media.53 Print permanence and durability can be improved by lamination. Prints on nanoporous media can be laminated and used immediately because the ink vehicle does not leave the substrate. Pigment particles remain on the surface of nanoporous media because they are too large to penetrate through the protection layer. This can cause variations in image gloss between areas of different print density and color, particularly between image highlights and the midtones and shadows. Image highlights are unprinted areas (or areas with low ink density). These areas are dominated by the surface finish and color of the substrate. Midtones and shadows have higher ink density, and the filmforming characteristics of pigment inks can affect gloss in these regions. Gloss uniformity can be improved by printing pigment inks on HP photo papers with a semi-gloss, satin, or matte finish. HP's Gloss Enhancer used in the HP Designjet Z3200 Printers improves gloss uniformity by printing a colorless "ink" where needed to match gloss across the full range of colors and optical densities. 51 The prints are smudge-resistant and ready for use within shortly after printing. Complete evaporation of volatile components of the ink vehicle may take several hours or longer, depending on ambient temperature and humidity. 52 For example, HP Premium Instant-dry Gloss Photo Papers for HP Designjet Z3200 Printers. 53 See www.hp.com/go/supplies/printpermanence 54 This could occur if the wrong paper, for example one requiring a higher ink load, were selected in the printer driver. 18