1. Field of the Invention
This invention relates generally to substrates used in printing and, more particularly, this invention relates to coated papers useful in ink jet printing.
2. Description of Related Art
In ink jet printing, uniformly shaped droplets of aqueous or solvent based dye solutions are ejected from a nozzle onto a paper or other substrate. Ejection can be continuous, where drops are selected electrostatically for imaging, or of the drop on demand type where drops are produced only when needed, thus obviating the need for electrostatic deflection.
The paper and surface chemistry requirements for good print quality vary widely and may rely on coating materials to create appropriate ink sorption characteristics.
Ink jet inks may be water-based or may have an alkylene glycol or other solvent base.
For the printing of well shaped dots by means of ink jets, and especially for multi-color printing with ink jets, the use of paper coated with a pigment is highly desirable. The pigment and the binder of the coating ideally would serve a dual function: they both sorb the solvent of the ink (i.e., dry the ink) and hold the dye-stuff of the ink on the surface of the coating to maximize the visual effect of the ink.
In order to maximize visual effectiveness, the surface area of the pigment in the coating should be high. In this way, the maximum amount of dyestuff from the ink will be in the path of light reflected from the substrate to the eye, and a minimal amount of dyestuff will be absorbed into the pigment layer or the paper substrate.
Ideally, a binder used in a paper coating should serve the functions of holding the pigment so as to reduce or eliminate dusting or chalking thereof, as ink jet printers with very fine orifice nozzles are quite susceptible to clogging. Also, the binder should help in the sorption of the solvent of the ink. If too tight a binder is used, ink will remain on the surface and will smear or even splatter when hitting the surface after ejection from the nozzle. Too weak a binder will not hold the pigment without chalking.