Ink set for inkjet printing

1. An ink set comprising two or more aqueous pigment-based inks,

each aqueous pigment-based ink having at least 75 weight % and up to and including 95 weight % of water, and consisting essentially of:

a) one or more pigment colorants selected from cyan, yellow, magenta, and black pigments;

b) one or more water-miscible humectants that are present in a total amount of at least 3 weight % and up to and including 10 weight and wherein glycerol is not present or is present in an amount of less than 0.5 weight %;

and optionally,

c) an acidic polymer that is an anionic polyurethane, an acidic acrylic polymer, an acidic styrene-acrylic polymer, or any combination of these materials, each acidic polymer having an acid number of at least 50 and up to and including 240, and each acidic polymer being neutralized with sufficient base to render it dispersible or soluble in each aqueous pigment-based ink,

wherein the weight % amounts of water and the b) water-miscible humectants are based on the total weight of each aqueous pigment-based ink, and

wherein

when the a) one or more pigment colorants is a cyan pigment in an aqueous cyan pigment-based ink, the (b) one or more water-miscible humectants is 1,2-propanediol alone,

when the a) one or more pigment colorants is a magenta pigment in an aqueous magenta pigment-based ink, the (b) one or more water-miscible humectants is 1,2-propanediol alone, or 1,2-propandiol with 2-[2-(2-hydroxyethoxy)ethoxy]ethanol at a weight ratio of 1:1 and up to and including 8:1,

when the a) one or more pigment colorants is a yellow pigment in an aqueous yellow pigment-based ink, the (b) one or more water-miscible humectants is 1,2-propanediol alone, or 1,2-propanediol with 2-[2-(2-hydroxyethoxy)ethoxy]ethanol at a weight ratio of at least 1:1 and up to and including 8:1, and

when the a) one or more pigment colorants is a black pigment in an aqueous black pigment-based ink, the (b) one or more water-soluble humectants is 1,2-propanediol alone, or 1,2-propanediol with 2-[2-(2-hydroxyethoxy)ethoxy]ethanol at a weight ratio of at least 1:1 and up to and including 8:1.

2. The ink set of claim 1 , optionally further comprising an aqueous pigment-based ink comprising any one of a green pigment, an orange pigment, a white pigment, a red pigment, a blue pigment, or a violet pigment, and the total amount of a) one or more pigment colorants independently present in each of the optional aqueous pigment-based ink is at least 0.1 weight % and up to and including 25 weight %, based on the total weight of each optional aqueous pigment-based ink, and the b) one or more water-soluble humectants comprises 1,2-propanediol and no glycerol.

3. The ink set of claim 1 , wherein 50% of the volume of each of the a) one or more pigment colorants is provided by pigment colorant particles having a diameter of less than 100 nm, and 95% of the volume of eaCh of the a) one or more pigment colorants is provided by pigment colorant particles having a diameter of less than 150 nm, the particle size diameters being measured using a dynamic light scattering particle sizing instrument.

4. The ink set of claim 1 , wherein the b) one or more water-miscible humectants are present in a total amount of at least 4 weight % and up to and including 8 weight %, based on the total weight of each of the aqueous pigment-based inks, and glycerol is not present.

5. The ink set of claim 1 , wherein the b) one or more water-miscible humectants are present in a total amount of at least 5 weight % and up to and including 10 weight %, based on the total weight of each of the aqueous pigment-based inks, and glycerol is not present.

6. The ink set of claim 1 , wherein each of the two or more different aqueous pigment-based inks further comprises, independently, the c) acidic polymer.

7. The ink set of claim 1 , wherein at least one of the cyan, yellow, magenta and black pigment colorants is anionically-stabilized.

8. The ink set of claim 1 , wherein each cyan, yellow, magenta, and black pigment colorants is anionically-stabilized.

9. The ink set of claim 2 , wherein all of the pigment colorants present in each aqueous pigment-based ink are anionically-stabilized.

10. The ink set of claim 1 , wherein each of the two or more aqueous pigment-based inks independently has a dynamic viscosity lesa than or equal to 5 centipoise (5 mPa-sec) as measured at 25° C.

11. The ink set of claim 1 , comprising at least one aqueous cyan pigment-based ink, at least one aqueous magenta pigment-based ink, at least one aqueous yellow pigment-based ink, and at least one aqueous black pigment-based ink, each comprising the (b) one or more water-miscible humectants thus defined.

12. The ink set of claim 11 , wherein all of the a) one or more pigment colorants in each of the two or more different aqueous pigment-based inks are anionically-stabilized.

13. An aqueous pigment-based ink having at least 75 weight % and up to and including 90 weight % of water, and consisting essentially of:

a) one or more pigment colorants, wherein 50% of the volume of each of the a) one or more pigment colorants is provided by pigment colorant particles having a diameter of less than 100 nm, and 95% of the volume of each of the a) one or more pigment colorants is provided by pigment colorant particles having a diameter of less than 150 nm, the particle size diameters being measured using a dynamic light scattering particle sizing instrument;

b) one or more water-miscible humectants defined as follows, and glycerol is not present or is present at less than 0.5 weight % of glycerol; and

c) an acidic polymer that is an anionic polyurethane, an acidic acrylic polymer, an acidic styrene-acrylic polymer, or any combination of these materials, each acidic polymer having an acid number of at least 50 and up to and including 240, each acidic polymer being neutralized with sufficient base to render it dispersible or soluble in the aqueous pigment-based ink;

wherein the aqueous pigment-based ink is selected from the following:

an aqueous cyan pigment-based ink that comprises one or more anionically-stabilized cyan pigment colorants, and the b) one or more water-miscible humectants is only 1,2-propanediol, and that is present in a total amount of at least 4 weight % and up to and including 8 weight %;

an aqueous magenta pigment-based ink that comprises one or more anionically-stabilized magenta pigment colorants, and the b) one or more water-miscible humectants is of 1,2-propanediol alone, or 1,2-propanediol with 2-[2-(2-hydroxyethoxy)ethoxy]ethanol at a weight ratio of 1:1 and up to and including 8:1, and that is present in a total amount of at least 4 weight % and up to, and including 8 weight %;

an aqueous yellow pigment-based ink that comprises one or more anionically-stabilized yellow pigment colorants, and the b) one or more water-miscible humectants 1,2-propanediol alone, or 1,2-propanediol with 2-[2-(2-hydroxyethoxy)ethoxy]ethanol 1,2-butanediol, at a weight ratio of at least 1:1 and up to and including 8:1, and that are present in a total amount of at least 4 weight % and up to and including 8 weight %; and

an aqueous black pigment-based ink that comprises one or more anionically-stabilized black pigment colorants, and the b) one or more water-miscible humectants is 1,2-propanediol, or 1,2-propanediol with 2-[2-(2-hydroxyethoxy)ethoxy]ethanol, and that are present in a total amount of at least 5 weight % and up to and including 10 weight %,

all amounts being based on the total weight of the respective aqueous pigment-based ink.