Image forming set, image forming apparatus, and image forming method

1. An image forming set, comprising:

an aqueous ink comprising a colorant, a water-soluble organic solvent, and water; and

a post-treatment liquid comprising a water-soluble organic solvent, water, and at least one of a urethane resin and an acrylic resin,

wherein a solubility parameter of a mixed solution of the water-soluble organic solvent and the water in the post-treatment liquid is lower than a solubility parameter of a mixed solution of the water-soluble organic solvent and the water in the aqueous ink by 2.1 (cal/cm 3 ) 1/2 or greater.

2. The image forming set according to claim 1 , wherein the solubility parameter of the mixed solution of the water-soluble organic solvent and the water in the post-treatment liquid is lower than the solubility parameter of the mixed solution of the water-soluble organic solvent and the water in the aqueous ink by 7.5 (cal/cm 3 ) 1/2 or less.

3. The image forming set according to claim 1 , wherein a difference between a solubility parameter of the at least one of the urethane resin and the acrylic resin in the post-treatment liquid, and the solubility parameter of the mixed solution of the water-soluble organic solvent and the water in the post-treatment liquid is 4 (cal/cm 3 ) 1/2 or less.

4. The image forming set according to claim 1 , wherein the water-soluble organic solvent in the post-treatment liquid is at least one selected from the group consisting of 3-methoxy-1-butanol, 3-methoxy-3-methyl-1-butanol, diethylene glycol monoisopropyl ether, diethylene glycol monoisobutyl ether, tripropylene glycol methyl ether, 1-methoxy-2-propanol, a compound represented by the following formula (I), a compound represented by the following formula (II), and a compound represented by the following formula (III):

CH 3 O(CH 2 CHCH 3 O) 2 CH 3   Formula (I)

C 4 H 9 O(CH 2 CH 2 O) 2 CH 3   Formula (II)

CH 3 O(CH 2 CHCH 3 O) 3 CH 3   Formula (III), and

an amount of the water-soluble organic solvent in the post-treatment liquid is 20% by mass to 40% by mass relative to a total amount of the post-treatment liquid.

5. The image forming set according to claim 1 , wherein an amount of the at least one of the urethane resin and the acrylic resin in the post-treatment liquid is 10% by mass to 40% by mass relative to a total amount of the post-treatment liquid,

the urethane resin is an anionic self-emulsifying ether urethane resin, and

the acrylic resin is an acryl silicone resin.

6. The image forming set according to claim 1 , wherein the at least one of the urethane resin and the acrylic resin in the post-treatment liquid comprises at least two kinds of particles having different volume average particle diameters,

one of the at least two kinds of particles of the at least one of the urethane resin and the acrylic resin has a volume average particle diameter larger than a volume average particle diameter of the colorant in the aqueous ink, and

other of the at least two kinds of particles of the at least one of the urethane resin and the acrylic resin has a volume average particle diameter smaller than the volume average particle diameter of the colorant in the aqueous ink.

7. The image forming set according to claim 1 , wherein the post-treatment liquid further comprises wax having a melting point of 80° C. to 140° C., the wax comprising at least one of a polyethylene wax emulsion and carnauba wax, and

an amount of the wax is 1% by mass to 10% by mass relative to a total amount of the post-treatment liquid.

8. The image forming set according to claim 1 , the post-treatment liquid further comprises a self-crosslinking resin configured to crosslink with the at least one of the urethane resin and the acrylic resin, the self-crosslinking resin being an isocyanate group-containing resin, and

an amount of the self-crosslinking resin is 1% by mass to 10% by mass relative to a total amount of the post-treatment liquid.

9. The image forming set according to claim 1 , wherein the aqueous ink further comprises a fluorosurfactant.

10. The image forming set according to claim 1 , wherein the solubility parameter of the mixed solution of the water-soluble organic solvent and the water in the aqueous ink is 18 (cal/cm 3 ) 1/2 to 22 (cal/cm 3 ) 1/2 .

11. The image forming set according to claim 1 , wherein the solubility parameter of the mixed solution of the water-soluble organic solvent and the water in the post-treatment liquid is 10 (cal/cm 3 ) 1/2 to 30 (cal/cm 3 ) 1/2 .

12. The image forming set according to claim 1 , wherein the solubility parameter of the mixed solution of the water-soluble organic solvent and the water in the post-treatment liquid is lower than the solubility parameter of the mixed solution of the water-soluble organic solvent and the water in the aqueous ink by 3.0 (cal/cm 3 ) 1/2 to 5.0 (cal/cm 3 ) 1/2 .

13. The image forming set according to claim 1 , wherein a mass ratio of an amount (% by mass) of the water-soluble organic solvent to an amount (% by mass) of the water in the mixed solution in the aqueous ink is 0.5 to 2.

14. The image forming set according to claim 1 , wherein a mass ratio of an amount (% by mass) of the water-soluble organic solvent to an amount (% by mass) of the water in the mixed solution in the post-treatment liquid is 0.5 to 2.

15. The image forming set according to claim 1 , wherein a minimum film forming temperature of the urethane resin is 25° C. or lower.

16. The image forming set according to claim 1 , wherein the aqueous ink further comprises a fluorosurfactant, the fluorosurfactant being the compound represented by the following formula (i):

C 4 F 9 —CH 2 CH(OH)CH 2 O—(CH 2 CH 2 O) 8 —CH 2 CH(OH)CH 2 —C 4 F 9   Formula (i).

17. An image forming apparatus comprising:

an ink set comprising an aqueous ink and a post-treatment liquid, the aqueous ink comprising a colorant, a water-soluble organic solvent, and water, and the post-treatment liquid comprising at least one of a urethane resin and an acrylic resin, a water-soluble organic solvent, and water;

an image forming unit configured to jet the aqueous ink to a recording medium to form an image; and

a post-treatment unit configured to apply the post-treatment liquid onto a surface of the recording medium, on which the aqueous ink has been jetted,

wherein a solubility parameter of a mixed solution of the water-soluble organic solvent and the water in the post-treatment liquid is lower than a solubility parameter of a mixed solution of the water-soluble organic solvent and the water in the aqueous ink by 2.1 (cal/cm 3 ) 1/2 or greater.

18. The image forming apparatus according to claim 17 , further comprising a drying unit configured to dry the recording medium on which the post-treatment liquid has been applied by the post-treatment unit.

19. An image forming method comprising:

jetting an aqueous ink to a recording medium to form an image, where the aqueous ink comprises a colorant, a water-soluble organic solvent, and water; and

applying a post-treatment liquid onto a surface of the recording medium, on which the aqueous ink has been jetted, where the post-treatment liquid comprises at least one of a urethane resin and an acrylic resin, a water-soluble organic solvent, and water,

wherein a solubility parameter of a mixed solution of the water-soluble organic solvent and the water in the post-treatment liquid is lower than a solubility parameter of a mixed solution of the water-soluble organic solvent and the water in the aqueous ink by 2.1 (cal/cm 3 ) 1/2 or greater.

20. The image forming method according to claim 19 , wherein the post-treatment liquid is applied within 1 second to 3 seconds after the aqueous ink is jetted.