In recent years, computer printer technology has evolved to a point where very high-resolution images can be transferred to various media. One particular type of printing involves the placement of small drops of a fluid ink onto a surface in response to a digital signal. Typically, the fluid ink is placed or jetted onto the surface without physical contact between the printing device and the surface. The method that the ink is deposited onto the printing surface varies from system to system. However, two major systems include continuous ink deposit and drop-on-demand ink deposit.
With regard to continuous printing systems, inks used are typically based on solvents such as methyl ethyl ketone and ethanol. Essentially, continuous printing systems function as stream ink droplets are ejected and directed by printer nozzle. The ink droplets are directed additionally with the assistance of an electrostatic charging device in close proximity to the nozzle. If the ink is not used on the desired printing surface, the ink is recycled for later use. With regard to drop-on-demand printing systems, the ink-jet inks are typically based upon water and glycols. Essentially, with these systems, ink droplets are propelled from a nozzle by heat or by a pressure wave. Additionally, all of the ink droplets are used to form the printed image and are ejected when needed.
There are several reasons that ink-jet printing has become a popular way of recording images on various media, particularly paper. Some of these reasons include low noise, capability of high speed recording, and multi-color recording. Additionally, these advantages can be obtained at a relatively low price to consumers. However, though there has been great improvement in ink-jet printing, accompanying this improvement are increased demands on ink-jet printing, e.g., higher speed, higher resolution, full color image formation, etc.
There are several characteristics to consider when evaluating a printer ink in conjunction with a printing surface or substrate. Such characteristics include (a) edge acuity and optical density of the image on the surface, (b) dry time of the ink on the substrate, (c) adhesion to the substrate, (d) lack of deviation of ink droplets, (e) presence of all dots, (f) resistance of the ink after drying to water and other solvents, (g) long-term storage stability, and (h) long-term reliability without corrosion or nozzle clogging. Though the above list of characteristics provides a worthy goal to achieve, there are difficulties associated with satisfying all of the above characteristics. Often, the inclusion of an ink component meant to satisfy one of the above characteristics can prevent another characteristic from being met. Thus, most commercial inks for use in ink-jet printers represent a compromise in an attempt to achieve at least an adequate response in meeting all of the above listed requirements.
Papers used for ink-jet printing have typically included high-quality or wood-free papers designed to have a high ink absorptivity. These papers are functionally good for ink-jet printing because the ink-jet inks may be absorbed readily and dry quickly. However, such papers often do not allow for a crisp or sharp image.
In order to attain enhanced print quality and image quality as in a photograph, special media has been developed to work with aqueous inks. For example, various coated papers (art paper, coat paper, cast-coat paper, etc.) have been prepared by coating a layer comprising a hydrophilic binder and an inorganic pigment on a paper substrate. Additionally, recording sheets have been prepared by coating an ink absorptive layer on paper or other supports, e.g., transparent or opaque plastic film supports. An example of such specialty media utilizes a swelling-type ink absorptive layer, e.g., gelatin. Though swellable media provides a relatively good substrate with respect to certain image quality properties, a drawback includes the fact that swellable media requires longer dry-time than other types of media. Additionally, with some inks, swellable media performance is less than desirable with respect to humid hue shift and humid bleed. Because of these limitations, it has been recognized that it would be advantageous to develop methods for providing fast drying, high quality images that exhibit only minimal humid hue shift and humid bleed.