Ink-jet recording method and ink-jet recording apparatus

1. An ink-jet recording method for performing recording by discharging an ink from an ink-jet head onto a recording medium, the ink constructing an ink set for ink-jet recording which includes an achromatic color ink and at least three chromatic color inks, the method comprising:

formation of an achromatic color recording area in the recording medium by the achromatic color ink;

formation of a chromatic color recording area in the recording medium by at least one chromatic color ink selected from the at least three chromatic color inks; and

formation of a boundary area in the recording medium, the boundary area including a first achromatic color boundary area formed by the achromatic color ink and the at least three chromatic color inks, and a second achromatic color boundary area formed by the at least three chromatic color inks,

wherein the first achromatic color boundary area is located such that the first achromatic color boundary area is adjacent to the achromatic color recording area, and the second achromatic color boundary area is located such that the second achromatic color boundary area is adjacent to the chromatic color recording area; and

the boundary area is formed to have a width, in a direction from the achromatic color recording area toward the chromatic color recording area, of not more than 340 μm, and the second achromatic color boundary area is formed to have a width in the direction of not more than 170 μm.

2. The ink-jet recording method according to claim 1 , wherein each of the first achromatic color boundary area and the second achromatic color boundary area is formed to have a width in the direction of not more than 100 μm.

3. The ink-jet recording method according to claim 1 , wherein the formation of the first achromatic color boundary area and the formation of the second achromatic color boundary area are performed after performing either one of the formations of the achromatic color recording area and the chromatic color recording area, and before performing the other of the formations of the achromatic color recording area and the chromatic color recording area.

4. The ink-jet recording method according to claim 3 , wherein the formations of the achromatic color recording area, the chromatic color recording area, the first achromatic color boundary area and the second achromatic color boundary area, included in a recording area in which recording is performed when the ink-jet head is moved in a scanning direction, are performed while the ink-jet head is performing one scanning in the direction or an opposite direction opposite to the direction.

5. The ink-jet recording method according to claim 1 , satisfying the following condition (I):

K<C  Condition (I):

wherein in the condition (I),

K: surface tension of the achromatic color ink (mN/m); and

C: surface tension of the at least one chromatic color ink selected from the at least three chromatic color inks used for forming the chromatic color recording area (mN/m).

6. The ink-jet recording method according to claim 1 , wherein in the formation of the first achromatic color boundary area, an usage amount of the achromatic color ink is smaller than a total of usage amounts of the at least three chromatic color inks.

7. The ink-jet recording method according to claim 1 , wherein each of the achromatic color ink and the at least three chromatic color inks contains a pigment.

8. The ink-jet recording method according to claim 1 , further comprising color conversion of pixels corresponding to the boundary area into pixels using black, magenta, cyan and yellow and pixels using magenta, cyan and yellow, wherein the pixels corresponding to the boundary area are included in pixel data, of image data for ink-jet recording, including information of color used in pixels corresponding to recording area.

9. The ink-jet recording method according to claim 8 , wherein when the color conversion is performed, pixels, among the pixels corresponding to the boundary area, which are adjacent to the achromatic color recording area, are subjected to the color conversion into the pixels using black, magenta, cyan and yellow; and

when the color conversion is performed, pixels, among the pixels corresponding to the boundary area, which are adjacent to the chromatic color recording area, are subjected to the color conversion into the pixels using magenta, cyan and yellow.

10. An ink-jet recording apparatus which performs recording by discharging an ink toward a recording medium, the apparatus comprising:

an ink accommodating section configured to be accommodatable an ink set for ink-jet recording which includes an achromatic color ink and at least three chromatic color inks;

an ink jet head; and

a controller configured to control the ink-jet head to perform:

formation of an achromatic color recording area in the recording medium by using the achromatic color ink,

formation of a chromatic color recording area in the recording medium by using at least one chromatic color ink selected from the at least three chromatic color inks, and

formation of a boundary area in the recording medium, the boundary area including a first achromatic color boundary area formed by the achromatic color ink and the at least three chromatic color inks, and a second achromatic color boundary area formed by the at least three chromatic color inks;

the controller controlling the ink-jet head such that the first achromatic color boundary area is located adjacent to the achromatic color recording area and the second achromatic color boundary area is located adjacent to the chromatic color recording area; and that the boundary area is formed to have a width, in a direction from the achromatic color recording area toward the chromatic color recording area, of not more than 340 μm, and the second achromatic color boundary area is formed to have a width in the direction of not more than 170 μm.

11. The ink-jet recording apparatus according to claim 10 , wherein the controller controls the ink-jet head such that each of the first achromatic color boundary area and the second achromatic color boundary area is formed to have a width in the direction of not more than 100 μm.

12. The ink-jet recording apparatus according to claim 10 , wherein the controller controls the ink-jet head such that the ink-jet head performs the formation of the first achromatic color boundary area and the formation of the second achromatic color boundary area after performing either one of the formations of the achromatic color recording area and the chromatic color recording area, and before performing the other of the formations of the achromatic color recording area and the chromatic color recording area.

13. The ink-jet recording apparatus according to claim 12 , wherein the controller controls the ink-jet head such that the ink-jet head performs the formations of the achromatic color recording area, the chromatic color recording area, the first achromatic color boundary area and the second achromatic color boundary area, included in a recording area in which recording is performed when the ink-jet head is moved in a scanning direction, while the ink-jet head is performing one scanning in the direction or an opposite direction opposite to the direction.

14. The ink-jet recording apparatus according to claim 10 , satisfying the following condition (I):

K<C  Condition (I):

wherein in the condition (I),

K: surface tension of the achromatic color ink (mN/m); and

C: surface tension of the at least one chromatic color ink selected from the at least three chromatic color inks used for forming the chromatic color recording area (mN/m).

15. The ink-jet recording apparatus according to claim 10 , wherein in the formation of the first achromatic color boundary area, the controller controls the ink-jet head such that an usage amount of the achromatic color ink is smaller than a total of usage amounts of the at least three chromatic color inks.

16. The ink-jet recording apparatus according to claim 10 , wherein each of the achromatic color ink and the at least three chromatic color inks contains a pigment.

17. The ink-jet recording apparatus according to claim 10 , wherein the controller is configured to perform color conversion of pixels corresponding to the boundary area into pixels using black, magenta, cyan and yellow and into pixels using magenta, cyan and yellow, wherein the pixels corresponding to the boundary area are included in pixel data, of image data for ink-jet recording, including information of color used in pixels corresponding to recording area.

18. The ink-jet recording apparatus according to claim 17 , wherein when performing the color conversion, the controller performs color conversion of pixels, among the pixels included in the pixel data used for the recording and constructing the boundary area, which are adjacent to the achromatic color recording area, into the pixels using black, magenta, cyan and yellow; and

when performing the color conversion, the controller performs color conversion of pixels, among the pixels included in the pixel data used for the recording and constructing the boundary area, which are adjacent to the chromatic color recording area, into the pixels using magenta, cyan and yellow.