Method of printing pigment-based inks including ink sets, inks and printers therefor
A method of inkjet printing includes the steps of: printing a first ink onto a print medium, the first ink including a first self-dispersible pigment, the first ink having a first pigment content A; and subsequently printing a second ink onto the print medium at least partially over the first ink, the second ink including a second pigment and a polymeric dispersant encapsulating the second pigment, the second ink having a second pigment content B. The first self-dispersible pigment and the second pigment have a same color; the pigment content A of the first ink and the pigment content B of the overprinted second ink have a relationship 0.8≦A/B≦1.2; and a polymer acid value of the polymeric dispersant is in the range of 100 to 170.
1. A method of inkjet printing comprising the steps of:
printing a first ink onto a print medium, the first ink comprising a first self-dispersible pigment in an amount A in terms of a wt. % of the first ink; and
subsequently printing a second ink onto the print medium at least partially over the first ink, the second ink comprising a second pigment in an amount B, in terms of a wt. % of the second ink, and a polymeric dispersant encapsulating the second pigment;
wherein:
the first self-dispersible pigment and the second pigment have a same color;
the amount A of the first pigment and the amount B of the second pigment have a relationship 0.8≦A/B≦1.2;
a polymer acid value of the polymeric dispersant is in the range of 100 to 170 KOH mg/g; and
a weight-average molecular weight of the polymeric dispersant is in the range of 20,000 to 200,000.
2. The method of claim 1 , wherein ejected droplet weights of the first ink and the second ink are in the range of 1 ng to 5 ng per droplet, and a difference in droplet weights between the first ink and the second ink is less than 0.3 ng per droplet.
3. The method of claim 1 , wherein the second ink is printed over the first ink within a period of less than 10 milliseconds.
4. The method of claim 1 , wherein the first self-dispersible pigment and the polymeric dispersant encapsulating the second pigment have a same surface polarity.
5. The method of claim 1 , wherein the first self-dispersible pigment is a surface-modified derivative of the second pigment.
6. The method of claim 1 , wherein the first self-dispersible pigment comprises hydrophilic groups directly bonded to a pigment surface.
7. The method of claim 6 , wherein the first self-dispersible pigment comprises carboxylate groups directly bonded to the pigment surface, the first self-dispersible pigment being obtainable via oxidation of the second pigment.
8. The method of claim 1 , wherein at least the first ink comprises trimethylolpropane.
9. The method of claim 8 , wherein at least the first ink further comprises triethylene glycol.
10. The method of claim 1 , wherein the first and second inks comprise the same co-solvents.
11. The method of claim 1 , wherein the viscosities at 35° C. of the first ink and the second ink are in the range of 1.5 mPa·s to 4.0 mPa·s, and wherein a difference in viscosities at 35° C. between the first ink and the second ink is less than 0.5 mPa·s.
12. The method of claim 1 , wherein the surface tensions at 20° C. of the first ink and the second ink are in the range of 28 mN/m to 40 mN/m, and a difference in surface tensions at20 ° C. between the first ink and the second ink is less than 3 mN/m.
13. The method of claim 1 , wherein the amount A and the amount B are each in the range of 2 wt % to 7 wt %.
14. An ink set for an inkjet printer comprising:
a first ink comprising a first self-dispersible pigment in an amount A in terms of a wt. % of the first ink; and
a second ink comprising a second pigment in an amount B, in terms of a wt. % of the second ink, and a polymeric dispersant encapsulating the second pigment,
wherein:
the first self-dispersible pigment and the second pigment have a same color;
the amount A of the first pigment and the amount B of the second pigment have a relationship 0.8≦A/B≦1.2;
a polymer acid value of the polymeric dispersant is in the range of 100 to 170 KOH mg/g; and
a weight-average molecular weight of the polymeric dispersant is in the range of 20,000 to 200,000.
15. The ink set of claim 14 , wherein the first and second inks have one or more of the following physical properties:
the viscosities at 35° C. of the first ink and the second ink are in the range of 1.5 mPa·s to 4.0 mPa·s;
a difference in viscosities at 35° C. between the first ink and the second ink is less than 0.5 mPa·s;
the surface tensions at 20° C. of the first ink and the second ink are in the range of 28 mN/m to 40 mN/m; and
a difference in surface tensions at 20° C. between the first ink and the second ink is less than 3 mN/m.
16. The ink set of claim 14 , wherein at least the first ink comprises one or more co-solvents selected from the group consisting of: triethylene glycol and trimethylolpropane.