Causes and Solutions of Printhead Color Deviation: Analyzing Color Depth, Printhead Alignment, and Droplet Size
Explanation of Color Depth
Generally speaking, standard KCMY inks achieve color through the absorption and reflection of certain wavelengths of natural light.
We can use the three primary colors of light (RGB) to explain the color formation principle of KCMY inks. For example, cyan (C) ink absorbs red (R) light and reflects blue (B) and green (G) light, forming the color cyan. The table below shows the resulting colors formed by different inks and ink combinations:
| Ink | Absorbed Light | Reflected Light | Description |
|---|---|---|---|
| None | None | Red, Green, Blue — R+G+B | White |
| Black K | Red, Green, Blue — R+G+B | None | Black |
| Cyan C | Red — R | Green, Blue — G+B | Cyan |
| Magenta M | Green — G | Red, Blue — R+B | Magenta |
| Yellow Y | Blue — B | Red, Green — R+G | Yellow |
| C+M | Red, Green — R+G | Blue — B | Blue |
| C+Y | Red, Blue — R+B | Green — G | Green |
| M+Y | Green, Blue — G+B | Red — R | Red |
| C+M+Y | Red, Green, Blue — R+G+B | None | Black |
Explanation of Color Depth
The depth of the printed color is determined by the number of ink droplets deposited on the material. If there are exposed white areas, the light cannot be fully absorbed, and the color will change. Therefore, the size of ink droplets from different nozzles determines the ink coverage rate on the material, which in turn affects the depth of the printed color.
Another situation that affects our visual color perception is the distribution of lines or dots.
- If the lines or dots are evenly distributed, the color will appear uniform.
- If the lines or dots are unevenly distributed, the color will appear different.
As shown in the images below, the two patterns have the same line width and quantity, but visually, the pattern on the left appears lighter than the one on the right.
Factors Affecting Printhead Color Difference
The biggest factor is the physical position of the printhead, followed by the ink droplet size of the printhead. The least influential factor is the printhead color mixing.
Printhead Physical Position
For the I3200 printhead, one head contains four colors, each color has two rows. The sequence of the nozzles is arranged symmetrically. If the alignment is not good during printing, it may result in misaligned color rows.
The normal state of the eight nozzle rows is shown in the diagram below:
Factors Affecting Printhead Color Deviation
When the printhead is not vertical, the printhead may undergo the following changes:
• State after counterclockwise rotation of the printhead:
• State after clockwise rotation of the printhead:
In the above three situations, the printed color blocks of the same color rows will have obvious differences between exposed white areas and non-exposed white areas.
1. Normal state of ink droplets from the printhead:
2. State after counterclockwise rotation of the printhead:
3. State after clockwise rotation of the printhead:
4. When the printhead rotation angle is too large:
As shown in the four physical states of the printhead above:
1. In the normal state (①), the two rows of different colors align perfectly. The ink droplets cover the material best, and the single-pass print leaves fewer exposed white areas. Therefore, the color on the material is the most accurate.
2. In states ② and ③, both rows of ink droplets overlap at the same position. As a result, more than half of the material shows exposed white areas. Thus, the printed color on the material will appear much lighter than normal.
3. In state ④, when the printhead rotation angle is too large, the outer K and C rows may overlap at the best alignment point, but the M and Y rows cannot align properly. Therefore, the MY colors will appear darker than normal, while the KC colors will be normal.