Ink set and image forming device

1. An ink set comprising:

black ink having a static surface tension A; and

yellow ink having a static surface tension B,

wherein the static surface tension A is by 0.6 mN/m or more greater than the static surface tension B,

wherein the ink set is used in an image forming device including an inkjet head including a nozzle plate including a first nozzle array and a second nozzle array disposed adjacent to the first nozzle array, the first nozzle array including multiple first nozzles configured to discharge the black ink and a second nozzle array including multiple second nozzles configured to discharge the yellow ink,

wherein each nozzle of the multiple first nozzles and the multiple second nozzles has a cylindrical portion having a length of 25 μm or longer along an axial direction with an opening on an ink discharging side of the nozzle plate.

2. The ink set according to claim 1 , wherein the length is 30 μm or longer.

3. The ink set according to claim 1 ,

wherein the nozzle plate further includes respective first introduction portions configured to communicate with the multiple first nozzles and respective second introduction portions configured to communicate with the multiple second nozzles,

wherein a diameter of the respective first introduction portions is larger than a diameter of the multiple first nozzles and a diameter of the respective second introduction portions is larger than a diameter of the multiple second nozzles.

4. The ink set according to claim 1 ,

wherein the static surface tension A is by 0.7 mN/m or more greater than the static surface tension B.

5. The ink set according to claim 1 ,

wherein the following inequality is satisfied:

0.7 mN/m≤(the static surface tension A )−(the static surface tension B )≤1.0 mN/m.

6. The ink set according to claim 1 ,

wherein each of the black ink and the yellow ink comprises an acetylene glycol compound, triethylene glycol monobutyl ether, and glycerin,

wherein the following inequalities are satisfied:

|(proportion of the acetylene glycol compound in the black ink)−(proportion of the acetylene glycol compound in the yellow ink)|≤2 percent by mass,

|(proportion of triethylene glycol monobutyl ether in the black ink)−(proportion of triethylene glycol monobutyl ether in the yellow ink)|≤2 percent by mass,

|(proportion of glycerin in the black ink)−(proportion of glycerin in the yellow ink)|≤2 percent by mass.

7. The ink set according to claim 1 , wherein the ink head comprises a line-type inkjet head.

8. An image forming device comprising:

black ink having a static surface tension A;

yellow ink having a static surface tension B; and

an inkjet head including a nozzle plate including a first nozzle array and a second nozzle array disposed adjacent to the first nozzle array, the first nozzle array including multiple first nozzles configured to discharge the black ink and a second nozzle array including multiple second nozzles configured to discharge the yellow ink,

wherein each nozzle of the multiple first nozzles and the multiple second nozzles has a cylindrical portion having a length of 25 μm or longer along an axial direction with an opening on an ink discharging side of the nozzle plate,

wherein the static surface tension A is by 0.6 mN/m or more greater than the static surface tension B.

9. The image forming device according to claim 8 ,

wherein the length is 30 μm or longer.

10. The image forming device according to claim 8 ,

wherein the nozzle plate further includes respective first introduction portions configured to communicate with the multiple first nozzles and respective second introduction portions configured to communicate with the multiple second nozzles,

wherein a diameter of the respective first introduction portions is larger than a diameter of the multiple first nozzles and a diameter of the respective second introduction portions is larger than a diameter of the multiple second nozzles.

11. The image forming device according to claim 8 ,

wherein the static surface tension A is by 0.7 mN/m or more greater than the static surface tension B.

12. The image forming device according to claim 8 , wherein the following inequality is satisfied:

0.7 mN/m≤(the static surface tension A )−(the static surface tension B )≤1.0 mN/m.

13. The image forming device according to claim 8 ,

wherein each of the black ink and the yellow ink comprises an acetylene glycol compound, triethylene glycol monobutyl ether, and glycerin,

wherein the following inequalities are satisfied:

|(proportion of the acetylene glycol compound in the black ink)−(proportion of the acetylene glycol compound in the yellow ink)|≤2 percent by mass,

|(proportion of triethylene glycol monobutyl ether in the black ink)−(proportion of triethylene glycol monobutyl ether in the yellow ink)|≤2 percent by mass,

|(proportion of glycerin in the black ink)−(proportion of glycerin in the yellow ink)|≤2 percent by mass.

14. The image forming device according to claim 8 , wherein the ink head comprises a line-type inkjet head.

15. An ink set comprising:

dark color ink having a static surface tension A; and

light color ink having a static surface tension B,

wherein the static surface tension A is by 0.6 mN/m or more greater than the static surface tension B,

wherein the ink set is used in an image forming device including an inkjet head including a nozzle plate including a first nozzle array and a second nozzle array disposed adjacent to the first nozzle array, the first nozzle array including multiple first nozzles configured to discharge the dark color ink and a second nozzle array including multiple second nozzles configured to discharge the light color ink

wherein each nozzle of the multiple first nozzles and the multiple second nozzles has a cylindrical portion having a length of 25 μm or longer along an axial direction with an opening on an ink discharging side of the nozzle plate.