Aqueous ink, ink set, image forming method and image forming apparatus
An aqueous ink used together with a black ink containing a self-dispersion pigment, wherein the aqueous ink contains a reactive component for destabilizing the dispersion state of the self-dispersion pigment, the dynamic surface tension of the aqueous ink at a lifetime of 30 milliseconds is 41 mN/m or more, and the dynamic surface tension of the aqueous ink at a lifetime of 500 milliseconds is from 28 mN/m or more to 38 mN/m or less as determined by a maximum bubble pressure method.
1. An aqueous ink to be used together with a black ink comprising a self-dispersion pigment, the aqueous ink comprising:
a reactive component for destabilizing a dispersion state of the self-dispersion pigment; and
a polyoxyethylene alkyl ether as a surfactant,
wherein a dynamic surface tension, at 25° C., of the aqueous ink at a lifetime of 30 milliseconds is 41 mN/m or more and a dynamic surface tension, at 25° C., of the aqueous ink at a lifetime of 500 milliseconds is from 28 mN/m or more to 38 mN/m or less as determined by a maximum bubble pressure method, and wherein the content (% by mass) of the surfactant in the aqueous ink is from 0.10% by mass or more to 3.0% by mass or less based on the total mass of the ink.
2. The aqueous ink according to claim 1 , wherein the dynamic surface tension of the aqueous ink at a lifetime of 30 milliseconds determined by the maximum bubble pressure method is 51 mN/m or less.
3. The aqueous ink according to claim 1 , wherein the polyoxyethylene alkyl ether is at least one selected from surfactants represented by the following general formula (1) and surfactants represented by the following general formula (2)
wherein a, m and n each independently represent an integer of 1 or more, and m+n represents an integer of from 14 to 20:
wherein b, x and y each independently represent an integer of 1 or more, and x +y represents an integer of from 12 to 21.
4. The aqueous ink according to claim 1 , wherein the reactive component is a polyvalent metal.
5. An ink set comprising a plurality of inks, wherein the ink set comprises the aqueous ink according to claim 1 and the black ink according to claim 1 .
6. An image forming method using a black ink comprising a self-dispersion pigment and at least one aqueous ink to form an image,
wherein the aqueous ink being the aqueous ink according to claim 1 , the black ink being the black ink according to claim 1 ,
the method comprising forming an image in such a manner that an image formed with the black ink and an image formed with the aqueous ink overlap each other in at least a partial region.
7. An image forming apparatus for forming an image by using a black ink comprising a self-dispersion pigment and at least one aqueous ink,
wherein the aqueous ink being the aqueous ink according to claim 1 , the black ink being the black ink according to claim 1 ,
the apparatus comprising a unit for forming the image in such a manner that an image formed with the pigment ink and an image formed with the aqueous ink overlap each other in at least a partial region.
8. The aqueous ink according to claim 1 , wherein the HLB value of the surfactant as determined by the Griffin method is from 12.0 or more to 16.5 or less.