White Ink Mixing in Epson L18050 / ET-8550-Style DTF Conversions: Why It Happens and How to Reduce Cross-Contamination

Question 

I'm using an Epson L18050 that's been modified for DTF (similar to the ET-8550 style). I run a white ink circulation system. After I finish printing each day, I do maintenance and then shut the printer down-but I keep noticing that a small amount of ink mixes into the white ink.

My seller told me not to use cleaning solution on the capping station after printing (but I've been doing it daily). I also saw the "lock" idea mentioned, but I'm not using it because of the damper setup. Will using a lock solve my issue, and why am I getting this mixing problem?

Answer

What you're describing is ink cross-contamination, and in your specific routine it's most likely happening because the capping station is being kept "wet" (you're wet-capping) and/or because of pressure/level differences in the ink delivery system after shutdown.

Why white ink gets contaminated (most common causes)

Here are the main reasons this happens on L18050 / ET-8550-style DTF conversions:

1. Wet-capping can "share" liquid between channels

   • When you add cleaning solution (or any fluid) onto the cap top, you're creating a wet surface where small amounts of ink can dissolve and migrate.

   • If the head parks and seals on a cap top that's overly wet, the cap can act like a "mixing puddle." Over hours (overnight), tiny amounts of neighboring color residue can wick or smear into the fluid that later contacts the nozzles again-especially when circulation or priming starts next day.

   • That's why your seller says not to use cleaning solution there daily. It's not that cleaning solution is "bad"-it's that too much fluid in the wrong place at the wrong time encourages mixing.

2. Pressure imbalance and siphoning after shutdown

   • DTF setups often have bottles/tanks, dampers, adapters, and circulation loops that create uneven backpressure.

   • If one bottle sits slightly higher, is fuller, warmer, or has a different venting condition, it can slowly push ink when the printer is off.

   • White ink is especially sensitive because it's heavier (pigment loads), circulation lines are active, and the system sometimes "self-drifts" if not perfectly balanced.

3. White circulation can tug on the system

   • A circulation loop can create subtle pressure changes, especially if it runs near shutdown or if the system is still equalizing when you power off.

   • If there's any imperfect seal at the cap top, wiper area, or head parking alignment, circulation/pressure changes can increase the chance of cap-top transfer.

Is it "normal"?

A small amount of cross-contamination after wet-capping can be common on modified DTF systems, especially if you're wetting the cap top daily. So yes-this can be normal behavior, but that doesn't mean you can't reduce it.

What to do (practical fixes that usually help)

1) Don't over-wet the capping station

• If you must clean the cap top area:

  • Clean the surrounding area and wiper gently, but avoid leaving a puddle sitting on the cap.

  • If you applied solution, blot excess so the cap is damp-clean, not soaked.

• A good rule: the cap top should be clean and flexible, but not acting like a "reservoir."

2) Keep ink levels consistent before shutdown (very important)

This matches your proposed answer and it's one of the most effective habits:

• Try to keep all bottles at roughly the same ink level, especially before you leave.

• If one color bottle is much fuller than another, it can create a pressure advantage and slowly feed.

• Before shutdown, topping up so levels are even can reduce the chance of overnight drift/mixing.

3) Use a clip / shutoff on the lines (your "lock" idea)

Yes-some form of line lock can help, and it's exactly for the reason you suspected: it prevents slow siphoning/creeping flow when the printer is idle.

• A simple tube clip (or proper in-line shutoff) on the supply lines can stop the system from equalizing through the head/cap area.

• The important part is using it safely:

  • Do not clamp too hard (you can deform tubing permanently).

  • If you use a shutoff, remember to reopen it before printing (sounds obvious, but it's a very common mistake that causes starvation and head damage).

• About "because of the damper": dampers can reduce pulsing and help regulate flow, but they don't always prevent slow migration caused by gravity, venting differences, and capillary action-especially overnight.

4) Check venting and bottle height consistency

• Make sure every tank/bottle is venting in a consistent way (same style vent plug/air hole behavior).

• Keep bottles at the same physical height relative to the printhead. Even small differences can matter over many hours.

5) Inspect the cap top and wiper condition

If the cap top is:

• warped,

• swollen,

• not sealing evenly,

• or the wiper is dragging ink across the underside of the head,

...then you'll see more contamination. A worn cap top can also allow more "sharing" of fluid/ink residue.

About error codes

You didn't mention any printer error codes (for example, service codes, paper/ink system errors, or maintenance box warnings). If your printer is showing any codes during this issue, those codes matter-because they can point to sensor, pump/cap, or maintenance-related faults that worsen ink migration. For now, based on your description, this sounds like a mechanical/flow/maintenance routine issue rather than a specific code-triggered failure.

Addressing printer issues can get complicated because these problems are very hands-on and depend on small physical details (ink levels, tubing height, cap-top condition, seals, and daily routine). Because of that, we're not able to provide remote troubleshooting, step-by-step repair instructions, or direct repair support through messages. We do offer an in-person evaluation and repair service through our local diagnostic facility: Printer Repair Service (https://bchtechnologies.com/printer-repair-service). Due to high demand, we operate on a first-come, first-served basis, and it can take a few weeks before we're able to accept a drop-off. Our services are structured to repair either the whole printer or specific parts with clear intake instructions. That said, we understand our rates may not be the most economical-so we strongly recommend self-help through online research. A great starting point is YouTube, including our channel homepage: BCH Technologies on YouTube (https://youtube.com/@bchtechnologies). To find the most relevant videos quickly, use the search icon near the "About" area on the right side of the menu bar. I receive dozens of requests daily asking if I have a video on a specific topic, and after making videos for years it's hard to remember every single one-YouTube search is the fastest route. You may also get helpful recommendations from other creators that match your exact setup.

Thanks again for reaching out and for watching our videos-it really does help us improve. If you keep ink levels balanced and avoid wet-capping too heavily, you should see the white contamination reduce noticeably.