Ink set, inkjet recording method, ink medium set, and printing medium
An ink set which includes a first ink composition that contains a coloring agent, a surfactant in an amount of A1 mass %, a hydrophobic organic solvent in an amount of A2 mass %, and water, the first ink composition being used to form a first image, and a second ink composition that contains a coloring agent, a surfactant in an amount of B1 mass %, a hydrophobic organic solvent in an amount of B2 mass %, and water, the second ink composition being used to form a second image on the first image. The surfactant is a specific silicone-based surfactant; the octanol/water partition coefficient of the hydrophobic organic solvent is not less than 2.00 but less than 3.50; and the following formula 0.05≤(0.5×(B1−A1)+(B2−A2))≤0.70 is satisfied.
1 . An ink set comprising:
a first ink composition comprising a first colorant, a first surfactant, a first hydrophobic organic solvent, and water; and
a second ink composition comprising a second colorant, a second surfactant, a second hydrophobic organic solvent, and water, and applied to a first image formed using the first ink composition to form a second image, wherein
the first and second surfactants are each independently a silicone-based surfactant represented by formula (1):
wherein in the formula (1), R 1 and R 2 each independently represents a hydrogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 3 carbon atoms, a is an integer of 1 to 80, x and y are each independently an integer of 1 to 4, m and n are each independently an integer of 1 to 50, o and p are each independently an integer of 0 to 40, a sum of m and n is 2 to 100, and a sum of o and p is 0 to 80,
the first and second hydrophobic organic solvents each have a water-octanol partition coefficient of 2.00 or more and less than 3.50, and
when a content of the first surfactant in the first ink composition is designated as A1 (% by mass), a content of the first hydrophobic organic solvent in the first ink composition is designated as A2 (% by mass), a content of the second surfactant in the second ink composition is designated as B1 (% by mass), and a content of the second hydrophobic organic solvent in the second ink composition is designated as B2 (% by mass), a condition expressed by equation (2) is satisfied:
0.05≤[0.5×( B 1− A 1)+( B 2− A 2)]≤0.70 (2).
2 . The ink set according to claim 1 , wherein in the formula (1), m and n are each independently an integer of 1 to 30.
3 . The ink set according to claim 1 , wherein one or both of the first ink composition and the second ink composition comprise a binder.
4 . The ink set according to claim 3 , wherein the binder is at least one selected from the group consisting of a wax and a (meth)acrylic polymer.
5 . The ink set according to claim 4 , wherein the wax is at least one selected from the group consisting of a polyalkylene wax, an oxidized polyalkylene wax, and a paraffin wax.
6 . The ink set according to claim 4 , wherein the wax is an oxidized polyethylene wax.
7 . An inkjet printing method using the ink set according to claim 1 , the method comprising:
ejecting droplets of the first ink composition, and attaching the droplets to a printing medium to form a first image; and
ejecting droplets of the second ink composition, and attaching the droplets to the printing medium having the first image formed thereon to form a second image.
8 . An ink and medium set comprising the ink set according to claim 1 , and a printing medium.
9 . A printed medium comprising a first image formed by applying the first ink composition comprised in the ink set according to claim 1 , and a second image formed on the first image by applying the second ink composition comprised in the ink set.