Patent ID: 7273898

Claim:
An ink jet recording ink containing water and a colorant comprising a pigment encapsulated by a polymer having a carboxyl group, wherein said ink jet recording ink further contains at least methylisothiazolone and octylisothiazolone, wherein the octylisothiazolone content is at least 100 ppm and no more than 800 ppm, the combined amount of methylisothiazolone and octylisothiazolone is at least 110 ppm and no more than 1300 ppm, and wherein the methylisothiazolone content is at least 10 ppm and no more than 500 ppm, and is an amount that, in consideration of the octylisothiazolone content and the combined amount of methylisothiazolone and octylisothiazolone, would result in the ink having a final viscosity after storage in a stoppered vial for 30 days at 70° C. that is at least 1.0 and no more than 1.2 times greater than viscosity of the ink before the storage.