What are the methods for clearing clogged printheads in photo printers? What are the maintenance procedures?

What are the methods for dealing with clogged print heads in large-format printers?

Methods for Handling Clogged Print Heads

During printing, if a large-format printer's print head fails to eject ink properly, resulting in missing colors on the printed image, this is commonly referred to as "print head clogging." This issue particularly affects machines like the SAI Angel series and significantly impacts print quality and production yield. Understanding the causes of clogging helps improve machine operation and enhance print quality.

The working principle of a print head resembles that of a common bicycle pump: the reciprocating metal rod inside the pump corresponds to the core component of the print head—the piezoelectric crystal. When a pump fails to deliver air, there are generally two reasons: either the air passage is blocked or the piston rod is malfunctioning.

Print heads are far more complex than bicycle pumps, so the causes of clogging vary widely. The main types include:

1. Ink accumulation outside the print head nozzle: This is the most common form of clogging. Since solvents in ink must evaporate into the air to dry the print, ink is inherently volatile and tends to lose solvent and leave solid residue over time. During printing, some ink always remains around the nozzle. As it dries in the air, this residue gradually narrows or even blocks the nozzle opening. However, since this blockage occurs externally, it can be easily cleaned—hence the frequent need for print head cleaning.

2. Damaged piezoelectric crystal: A damaged crystal will definitely prevent ink ejection. Most piezoelectric print heads last about one year under normal use; however, in high-volume printing environments, they may fail before that, which is considered normal.

3. Piezoelectric crystal fatigue: This manifests as intermittent ink ejection—sometimes ink comes out, sometimes not—especially noticeable when printing dark images requiring larger ink volumes. In such cases, replacing the print head is often the best solution.

4. Clogged internal filter or ink channel: After prolonged use, especially in facilities where printing jobs are infrequent and machines are frequently shut down overnight, ink may remain stagnant inside the print head. Over time, it can adhere to the internal filter or walls of the ink channels, reducing the cross-sectional area through which ink flows and ultimately causing ink failure. 

5. Excessive or insufficient ink viscosity: If ink is too viscous, its flowability decreases, leading to insufficient ink output per unit time. Conversely, if ink is too thin (too diluted), air may be drawn into the nozzle during the piezoelectric crystal’s retraction phase instead of ink, resulting in air being ejected rather than ink. Both conditions lead to no ink output. To avoid this, users should store ink under recommended environmental conditions and allow it to acclimate for at least 24 hours before use. Low temperatures increase viscosity, while high temperatures reduce it. Significant differences in viscosity between batches of ink can cause clogging when mixed.

6. Drive circuit failure: Aging electronic components or excessive buildup of dried ink residue in the drive circuit can affect the voltage supplied to the print head, resulting in inconsistent or failed ink ejection.

7. Type of ink used: Some manufacturers produce ink with an improper balance of drying agents, causing it to dry too quickly. This increases the risk of external clogging. Although cleanable, frequent cleaning is required. If the print head is left unused for extended periods without proper maintenance, permanent damage may occur upon subsequent use.

8. Frequent ink changes: Improper handling during ink replacement often leads to inadequate protection of the print head, negatively affecting its performance.

9. Environmental temperature and humidity: Optimal operating conditions are typically 22–25°C temperature and 40–70% humidity. Deviations from these ranges alter ink viscosity, potentially causing ink starvation and misdiagnosis as "clogged print head."

10. Nozzle driving voltage: Appropriate nozzle voltage ensures smoother ink ejection.

Ink Thickening Issue

Low winter temperatures are an external factor causing ink to thicken. The change in ink consistency due to temperature is a physical phenomenon—only the form changes, not the essence (the fundamental properties of the ink).

When ink becomes too thick and viscous, it's best not to adjust its viscosity using thinners or ink additives. When users need to modify ink characteristics, the total amount of additives that original ink from manufacturers can accommodate is limited. Exceeding this limit may compromise the ink’s basic performance, even if usable, ultimately affecting print quality. Additionally, ink viscosity and thickness are related, referring here to its inherent properties rather than just surface appearance.

To resolve ink thickening caused by low temperatures, use the following methods:

(1) Place the original ink container near a radiator or on a heating panel to allow gradual warming back to normal condition.

(2) For urgent needs, externally heat with boiling water: pour hot water into a basin and submerge the original ink container (or box), ensuring steam does not enter. Remove when water cools to around 27°C, open the lid, stir thoroughly before use. Workshop ambient temperature should ideally remain around 27°C.

What Are the Maintenance Methods?

To clean plotter nozzles, you will need distilled water, lint-free cleaning cloths, and a tray.

1. Soak the cloth in distilled water.
2. Gently absorb (do not wipe) the nozzle area at the bottom of the printhead 3 to 5 times with the damp cloth.

Repeat this process for all nozzles being cleaned. Use a clean section of the cloth for each printhead to prevent color mixing. Test the printhead to check for clogging.

If clogging persists, slightly warm the distilled water and place a small amount in the tray. (When placing the printhead in the tray, avoid water level exceeding 2 cm above the base, as leakage could reach behind the chip.)

Stand the printhead upright in the warm water. Wait 30 seconds, then dry the nozzle thoroughly before testing again.

Each printhead must be cleaned with clean water. Alternatively, ultrasonic cleaners can also be used for nozzle cleaning.

To clean the chip, use alcohol and cotton swabs or lint-free cloths.

Turn off the plotter power.

Soak the cloth or cotton pad in alcohol.

Gently wipe the chip located behind the printhead to remove dirt or dried ink.

Repeat this process for each printhead, ensuring a clean section of cloth or fresh cotton swab is used for every printhead. Remove the printhead from the carriage and gently wipe the contact strip on the carriage with a clean, damp cotton swab or cloth. After cleaning, reinstall the printhead, making sure they are properly seated.

Plotter Ink Cartridge Air Leak—

After completing ink suction, do not immediately remove the syringe. Wait 20 seconds to allow pressure to equalize before pulling it out, preventing air from entering.