Takizawa, Yoshihisa; Aoki, Makoto; Kurabayashi, Yutaka;

Ink set

Disclosed herein is an ink-jet recording process which comprises applying a first liquid at least containing a water-soluble resin having at least one carboxyl group or anhydride thereof, or sulfonic group per molecule to a recording medium and then applying an ink at least comprising water, an organic solvent, a dye, an alkali-soluble resin and an alkali to the portions where the first liquid has adhered, thereby forming an image. An ink set and an instrument for use in such a process are also disclosed.

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What is claimed is:

1. An ink set for ink-jet recording having a first, a second, a third and a fourth ink independently, each of the inks having a different color from each other, and being selected from the group consisting of a black ink and three color inks of yellow, magenta and cyan, wherein

(1) the first ink contains a water-soluble resin having at least one carboxyl group or anhydride thereof, or sulfonic group in a molecule thereof, and the first ink's pH (pH.sub.1) ranges from pH 1 to 6;

(2) the second ink's pH (pH.sub.2) ranges from pH 4 to 8, and the second ink contains

(a) a water-soluble resin having at least one carboxyl group or anhydride thereof, or sulfonic group in a molecule thereof, or

(b) an alkali-soluble resin and an alkali;

(3) the third ink contains an alkali-soluble resin and an alkali, and the third ink's pH (pH.sub.3) ranges from pH 6 to 10;

(4) the fourth ink contains an alkali-soluble resin and an alkali and the fourth ink's pH (pH.sub.4) ranges from pH 8 to 13; and the pHs of the first, second, third and fourth inks satisfy the relationship of pH.sub.1 <pH.sub.2 <pH.sub.3 <pH.sub.4.

2. The ink set according to claim 1, wherein the water-soluble resin is a naturally-occurring or a synthetic water-soluble resin which has at least one carboxyl group or anhydride thereof, or sulfonic group in a molecule, or a mixture thereof.

3. The ink set according to claim 1, wherein the water-soluble resin is a polymer obtained by using, as a monomer, at least one of acrylic acid, methacrylic acid, itaconic acid, maleic acid and maleic anhydride, or a copolymer synthesized from at least one of said monomers and at least one of hydrophilic monomers having a hydrophilic group including a hydroxyl, amide, amino, ether, pyrrolidone or ethyleneimine group in a molecule.

4. The ink set according to claim 1, wherein the alkali-soluble resin is a copolymer of a hydrophilic monomer unit end a hydrophobic monomer.

5. The ink set according to claim 1, wherein the water-soluble resin has a weight average molecular weight of from 1,000 to 500,000.

6. The ink set according to claim 1, wherein the alkali-soluble resin has a weight average molecular weight of from 1,000 to 100,000.