Aqueous ink set, ink jet recording method and ink jet recording apparatus

1. An aqueous ink set for ink jet comprising a combination of a first ink and a second ink,

wherein the first ink includes a self-dispersible pigment to a particle surface of which a functional group that includes a phosphonic acid group is bonded, and a redispersion viscosity of the first ink as measured according to the following procedure is 5 mPa·s or less,

wherein measurement of the redispersion viscosity being such that after 1.5 g of the first ink is stored for 15 hours under a temperature of 30° C. and a relative humidity of 10%, the first ink is added thereto in an amount of the thus-reduced mass followed by additional storing for 2 hours to thereby measure the viscosity of the resultant,

wherein the second ink includes an anionic dye, a lithium ion, and a sodium ion, and a total concentration of the lithium ion and the sodium ion in the second ink is 0.050 mol/L or more, and

wherein a proportion of a concentration of the lithium ion in the total concentration of the lithium ion and the sodium ion in the second ink is 45% or more to 85% or less.

2. The aqueous ink set according to claim 1 , wherein the total concentration of the lithium ion and the sodium ion in the second ink is 0.200 mol/L or less.

3. The aqueous ink set according to claim 1 , wherein a total concentration of monovalent cations in the second ink is 0.400 mol/L or less.

4. The aqueous ink set according to claim 1 , wherein the functional group bonded to the particle surface of the self-dispersible pigment includes two phosphonic acid groups.

5. The aqueous ink set according to claim 1 , wherein a counter ion of the functional group bonded to the particle surface of the self-dispersible pigment includes at least one of a sodium ion, a potassium ion, and an ammonium ion.

6. The aqueous ink set according to claim 1 , wherein the content ×(% by mass) of the self-dispersible pigment in the first ink and the total concentration M (mol/L) of the lithium ion and the sodium ion in the second ink satisfy the relation of the following expression (1):

x/M≦ 65  . . . (1).

7. The aqueous ink set according to claim 1 , wherein a molecular weight of the functional group is 1,500 or less.

8. The aqueous ink set according to claim 1 , wherein an introduced amount of the functional group is 0.08 mmol/g or more to 0.33 mmol/g or less.

9. The aqueous ink set according to claim 1 , wherein a structure of the functional group is —C 6 H 4 —CONH —CH(PO 3 [M 1 ] 2 ) 2 or —C 6 H 4 —SO 2 —NH —C 3 H 6 —C(OH)(PO 3 [M 1 ] 2 ) 2 , where M 1 is a sodium ion, a potassium ion, or an ammonium ion.

10. The aqueous ink set according to claim 1 , wherein the content (% by mass) of the pigment in the first ink is 1.00% by mass or more to 10.00% by mass or less based on the total mass of the ink.

11. The aqueous ink set according to claim 1 , wherein the content (% by mass) of the anionic dye in the second ink is 1.00% by mass or more to 6.00% by mass or less based on the total mass of the ink.

12. The aqueous ink set according to claim 6 , wherein x/M is 15 or more.

13. An ink jet recording method comprising:

a step of ejecting an ink from an ejection orifice of a recording head of an ink jet system to record an image on a recording medium; and

a step of capping the ejection orifice with a cap,

wherein the ink comprises an ink included in an aqueous ink set for ink jet which comprises a combination of a first ink and a second ink,

wherein the first ink includes a self-dispersible pigment to a particle surface of which a functional group that includes a phosphonic acid group is bonded, and a redispersion viscosity of the first ink as measured according to the following procedure is 5 mPa·s or less,

wherein measurement of the redispersion viscosity being such that after 1.5 g of the first ink is stored for 15 hours under a temperature of 30° C. and a relative humidity of 10%, the first ink is added thereto in an amount of the thus-reduced mass followed by additional storing for 2 hours to thereby measure the viscosity of the resultant,

wherein the second ink includes an anionic dye, a lithium ion, and a sodium ion, and a total concentration of the lithium ion and the sodium ion in the second ink is 0.050mol/L or more, and

wherein a proportion of a concentration of the lithium ion in the total concentration of the lithium ion and the sodium ion in the second ink is 45% or more to 85% or less.

14. An ink jet recording apparatus comprising:

an ink storage portion within which an ink is stored;

a unit for ejecting the ink from an ejection orifice of a recording head of an ink jet system to record an image on a recording medium; and

a cap for capping the ejection orifice,

wherein the ink comprises an ink included in an aqueous ink set for ink jet which comprises a combination of a first ink and a second ink,

wherein the first ink includes a self-dispersible pigment to a particle surface of which a functional group that includes a phosphonic acid group is bonded, and a redispersion viscosity of the first ink as measured according to the following procedure is 5 mPa·s or less,

wherein measurement of the redispersion viscosity being such that after 1.5 g of the first ink is stored for 15 hours under a temperature of 30° C. and a relative humidity of 10%, the first ink is added thereto in an amount of the thus-reduced mass followed by additional storing for 2 hours to thereby measure the viscosity of the resultant,

wherein the second ink includes an anionic dye, a lithium ion, and a sodium ion, and a total concentration of the lithium ion and the sodium ion in the second ink is 0.050 mol/L or more, and

wherein a proportion of a concentration of the lithium ion in the total concentration of the lithium ion and the sodium ion in the second ink is 45% or more to 85% or less.