Ink jet head

1. An ink jet printer, comprising:

an ink jet head comprising a first black nozzle column including a plurality of nozzles, a second black nozzle column including a plurality of nozzles and a color nozzle column including a plurality of nozzles; and

a carriage that equips with the ink jet head, the carriage moving from a first side to a second side and from the second side to the first side;

wherein the first black nozzle column discharges the black ink while the carriage is moving from the first side to the second side and does not discharge the black ink while the carriage is moving from the second side to the first side;

wherein the second black nozzle column discharges the black ink while the carriage is moving from the first side to the second side and does not discharge the black ink while the carriage is moving from the second side to the first side; and

wherein the single color nozzle column discharges the different colors of ink while the carriage is moving from the first side to the second side and from the second side to the first side.

2. The ink jet head according to claim 1 , wherein the plurality of nozzles of the second black nozzle column are formed at positions shifted from the plurality of nozzles of the first black nozzle column in the transportation direction at a pitch which is the half of the predetermined pitch.

3. The ink jet head according to claim 1 , wherein the color nozzle column includes a cyan group discharging cyan ink, a magenta group discharging magenta ink, and a yellow group discharging yellow ink.

4. The ink jet head according to claim 3 , wherein each of the magenta group and the yellow group includes the same number of nozzles as the cyan group.

5. The ink jet head according to claim 3 , wherein the cyan group is disposed at a position on the upstream side of the transportation direction with respect to the magenta group and the yellow group.

6. The ink jet head according to claim 3 , wherein the yellow group is disposed at a position on the downstream side of the transportation direction with respect to the cyan group and the magenta group.

7. The ink jet head according to claim 1 , wherein the plurality of nozzles of the second black nozzle column are formed at positions shifted from the plurality of nozzles of the first black nozzle column in a transverse direction perpendicular to the transportation direction by a distance corresponding to an integer multiple of print resolution.

8. The ink jet head according to claim 1 , wherein the plurality of nozzles of the color nozzle column are formed at positions shifted from the plurality of nozzles of the second black nozzle column in a transverse direction perpendicular to the transportation direction by a distance corresponding to an integer multiple of print resolution.

9. The ink jet head according to claim 1 , wherein the plurality of nozzles of the second black nozzle column are formed at positions shifted from the plurality of nozzles of the first black nozzle column in a transverse direction perpendicular to the transportation direction by a distance which corresponds to an integer multiple of print resolution, and wherein the plurality of nozzles of the color nozzle column are formed at positions shifted from the plurality of nozzles of the second black nozzle column by a distance which corresponds to an integer multiple of print resolution and which is larger than a distance between the plurality of nozzles of the first black nozzle column and the plurality of nozzles of the second black nozzle column in the transverse direction.

10. An ink jet printer, comprising:

an ink jet head including a first black nozzle column, a second black nozzle column and a color nozzle column; and

a carriage that equips with the ink jet head, the carriage moving from a first side to a second side and from the second side to the first side;

wherein the first black nozzle column has a plurality of nozzles arranged at a predetermined pitch in a transportation direction of a medium, the first black nozzle column discharging black ink while the carriage is moving from the first side to the second side and not discharging the black ink while the carriage is moving from the second side to the first side;

wherein the second black nozzle column has a plurality of nozzles arranged at the predetermined pitch in the transportation direction and located at positions shifted from the plurality of nozzles of the first black nozzle column in the transportation direction, the second black nozzle column discharging the black ink while the carriage is moving from the first side to the second side and not discharging the black ink while the carriage is moving from the second side to the first side; and

wherein the color nozzle column has a plurality of nozzles arranged at the predetermined pitch in the transportation direction and located at the same positions as the plurality of nozzles of the second black nozzle column in the transportation direction, the color nozzle column discharging different colors of ink from different groups of nozzles thereof while the carriage is moving from the first side to the second side and from the second side to the first side, each group including a predetermined number of nozzles consecutively disposed in the transportation direction.