Inkjet printing process
A process for printing an image includes printing a substrate with an aqueous inkjet ink and drying the printed image with a near-infrared drying system, wherein the inkjet ink is a yellow or magenta inkjet ink and comprises a yellow or magenta colorant and a distinct near-infrared absorbing compound. Inkjet ink sets for use with an inkjet printing system employing a near-infrared drying system in the process include at least a black ink and a yellow ink, wherein the yellow ink comprises a yellow colorant and dispersed nanoparticulate colloidal silica at a concentration of from 0.1 to about 10 wt %, and the black ink comprises a black colorant and dispersed nanoparticulate colloidal silica at a concentration of from 0 wt. % to at most ½ of the wt. % of the dispersed nanoparticulate colloidal silica in the yellow ink. Various embodiments provide a process for inkjet printing and drying inks with improved absorption in the near-IR region of the spectrum for improved drying performance of aqueous, hypsochromic inks, and an inkjet ink set with improved balanced near-IR drying of black and yellow inkjet inks.
1. A process for printing an image comprising the steps of printing an image on a substrate with an aqueous inkjet ink and drying the printed image with a near-infrared drying system, wherein the inkjet ink is a yellow or magenta inkjet ink and comprises a yellow or magenta colorant and a distinct near-infrared absorbing compound, and wherein the near-infrared absorbing compound is present in the ink in the form of an aqueous dispersion of nanoparticulate colloidal silica.
2. The process of claim 1 , wherein the nanoparticulate colloidal silica comprises non porous particles having an average particle size of less than 100 nm.
3. The process of claim 1 , wherein the nanoparticulate colloidal silica comprises non porous particles having an average particle size of less than 50 nm.
4. The process of claim 1 , wherein the aqueous dispersion of nanoparticulate colloidal silica comprises hydrated silica particles which are absorbing in the near-IR spectrum from 750 nm to 900 nm.
5. The process of claim 1 , wherein upon drying the nanoparticulate colloidal silica becomes relatively transparent to near-IR radiation.
6. The process of claim 1 , wherein the inkjet ink is a yellow inkjet ink.
7. The process of claim 6 , wherein the inkjet ink comprises dispersed yellow pigment particles.
8. The process of claim 1 , wherein the inkjet ink comprises dispersed yellow or magenta pigment particles.
9. The process of claim 8 , wherein the pigment particles are dispersed with a polymeric dispersant, are dispersed with a surfactant, are encapsulated dispersed pigments, or are self dispersed without the need for a separate dispersant.
10. The process of claim 1 , wherein the inkjet ink is printed in a continuous inkjet printing process comprising:
A) providing a main fluid supply of a continuous inkjet printer with the inkjet ink;
B) delivering the inkjet ink from the main fluid supply to a printhead and ejecting a continuous stream of the inkjet ink from the printhead which continuous stream is broken into spaced droplets; and
C) in response to electrical signals received from a control mechanism, controlling the spaced droplets to select between printing droplets for marking a substrate and nonprinting droplets that are collected and returned to the main fluid supply.
11. The process of claim 10 , wherein the inkjet ink printed on the substrate is dried with the near-IR drying system prior to subsequent further printing on the substrate with a further inkjet ink.
12. The process of claim 10 , wherein the substrate is further printed on the substrate with a black ink inkjet comprising a black colorant and either no dispersed colloidal silica particles or a lower concentration of colloidal silica particles than that of the yellow or magenta ink, and wherein the resulting printed substrate is dried with near-IR radiation after printing of both the yellow or magenta ink and the black ink.
13. The process of claim 12 , wherein the black colorant of the black ink comprises carbon black.
14. The process of claim 12 , wherein yellow or magenta ink printed on the substrate comprises from 0.1 to 10 wt % of colloidal silica particles and the black ink printed on the substrate inkjet comprises either no dispersed colloidal silica particles or comprises dispersed colloidal silica particles at a concentration of at most ½ of the wt. % of the dispersed colloidal silica in the yellow or magenta ink.
15. The process of claim 12 , wherein the substrate is transported through the printing and near-IR drying at a speed of at least 100 m/min.
16. The process of claim 1 wherein the substrate is further printed on the substrate with a black ink inkjet comprising a black colorant and either no distinct near-infrared absorbing compound or a lower concentration of distinct near-infrared absorbing compound than that of the yellow or magenta ink, and wherein the resulting printed substrate is dried with near-IR radiation after printing of both the yellow or magenta ink and the black ink.
17. The process of claim 16 , wherein the black colorant of the black ink comprises carbon black.
18. The process of claim 16 , wherein the substrate is transported through the printing and near-IR drying at a speed of at least 100 m/min.
19. The process of claim 1 , wherein the substrate is transported through the printing and near-IR drying at a speed of at least 10 m/min.