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Printhead alignment Tips and Tricks for HP Latex R Series

The printhead alignment process is important to guarantee good image quality of R series prints. There are many potential image quality defects, like graininess, banding, bleed, text and line quality, or white to color misalignment due to wrong printhead alignment practices.

This guide summarizes when printhead alignment should be performed, and makes recommendations about the alignment procedure to mitigate some related image quality issues.

More information and a description of manual and automatic printhead alignment calibrations is available in the User Guide (Chapter 8: Printer calibration).

When to perform alignment?
• When a printhead (PH) is replaced:

o If the KC PH is changed → align all PH (including optimizers, overcoat, and whites)
o If any other PH is changed → align that PH using manual alignment (ensuring the other PH are aligned). For more clarity about which section of the alignment plot should be aligned again, see page 119 of the User Guide.

• When a new substrate is loaded and the printhead-to-paper spacing changes significantly.

o The distance between the PH and the substrate surface adjusts automatically according to the media thickness. Some users modify this value to print from a higher distance and to prevent media crashes. In this case, PH alignment calibration needs to be done again at this new printhead-to-paper distance.

• When there are print-quality problems that could be caused by printhead misalignment.

Printhead alignment recommendations
1. Perform a nozzle check plot to ensure good nozzle health of all printheads. It is important to ensure that all PHs are in good status before alignment, otherwise wrong alignment parameters can be calibrated.

2. It is recommended to perform PH alignments (optimizer, colors, overcoat, and white) in the same media and at the same time if possible. Different media thicknesses and media expansion during PH alignment on different media types can cause wrong alignment and white to color misalignments in white modes. 

To get the best outcome from APA we recommend using white SAV (the whiter and glossier the better). If you use porous media, it is possible that the automatic calibration is not well done.
There are several options, the two most recommended are:

o SAV white for APA colors, and SAV black with MA for whites. It is recommendable to load these media types in the same position on the printing zone when performing printhead alignment
o PET clear film or clear SAV for manual alignment (MA) of all printheads

3. The order of the alignment is very important. First, align Colors (with either manual or automatic alignment), and then the white Printheads with manual alignment.
IMPORTANT: remember that every time you perform an APA all colors are aligned, so white printheads should be manually aligned afterward (if best white to color registration is needed), since black is the reference for all printheads.

4. If a CK PH is changed, all the PH should be realigned, including the White PH. The reference of pen to pen calibration is the black. For this reason, if we change CK PH all printheads should be realigned.

5. If white or optimizer printheads are swapped (due to nozzle health issues or user’s convenience) it is important that they are properly aligned again.

6. If after following all these guidelines white to color misalignment is still present, perform white choke (starting at 4 pixels, and increase it if needed) to hide white layer misregistration against color.
Ink choke functionality can be either selected in the RIP or in the IPS. It is important to ensure that no choke artifacts from RIP are created (blank spaces).

7. It is important to note that white choke will hide most misregistration defects, but for certain applications, and mostly due to media expansion, the defect might still be present. In those cases, reducing curing and printing temperatures, as well as changing to a more temperature stable media, can also help mitigating the issue.

8. If white to color misalignment (WTCM) is still present, and consistently in one direction, try to modify manually alignment parameters to force centering the WTCM. It is important to keep a picture of the original alignment values, since corrections are often opposite between OF and UF modes (because WTCM is shown in opposite directions depending on the mode). This is due to the firing order change in the print mode planes.

9. Main differences between APA (automatic PH alignment) vs MPA (manual PH alignment):

o APA aligns extra fluids (optimizer and overcoat) on the paper direction, but MPA does not
o APA corrects Theta Zeta deviations, and MPA does not
o APA corrects all dies, and MPA corrects one and applies the same values to the rest
o APA is unattended, and MPA is not
o APA takes around 25 minutes, and MPA around 15 minutes

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