Black channels filling with air during/after a clean - Hard to clear, resort to Little Charge. VJ-2638 Sublimation

[alexcim]

Hello All,

First time poster, long time reader. Looking forward to becoming an active member of the community.

I have owned a VJ-2638 now for about 8 months (received in Feb, inked up in April). I print paper and sublimate with it. It is inked up with Kiian Hi-Pro ink, and a Kiian bulk ink feeder. Everything after the bulk feeder is OEM Mutoh (ie - all the new gear that came with the printer). I only print one paper, which is a 100gsm 2.4m wide paper. Since April, I have run approx 6km of paper through it, so around 14,400sqm (155,000 sqft). I only print full length rolls, which were 100m (330ft) for the first 5km (16400 ft) and 75m (250ft) for the last 1km (3200ft).

Anyway, the summary of my experience is:

• When the machine print, it prints perfectly for full rolls
• I easily print full rolls after I get started
• I don't have issues leaving it unattended (how much trust I have in it) and often let prints finish overnight because they're such long rolls and it's relatively slow.
• I haven't had issues during prints, only during cleans
• Air gets sucked into the black and sometimes yellow channel

However, my issue is that when I do a clean, it (can) fill the black channels with air which results in a poor nozzle check after. Basically, let's say that I finish a print overnight, and I come in the next morning, I will do a nozzle check and the black channels will be perfect - but the CMY channels will be fuzzy. Obviously, to get going for the day, I will need to do a clean. When I do so, it sucks air into the black channels which I really struggle to clear up.

Some days, after a print has finished, I will do a Short clean and it will be fine right away - meaning that I'll be able to print right after that. Other days I'll need hours and hours and many many cleans to get it working. I mean like 10-20 cleans, a variety of different cleans (Short, Medium, Long) and a lot of time waiting between cleans for nozzles to clear up (I might start at 6am, and it's ready to print by 2pm). Other days, I'll have to resort to "Little Charges" to sort it, and that seems to always fix the issue.

I have attached a record of my experiences to date in the PDF. I have videos for each day showing what happens. It's very repetitive, so only a few videos in a row will show the issue well. Here is a video that highlights the typical experience: https://vimeo.com/753706616/79b0a3c61d

The machine is still under warranty, and I've had the company that I bought it from send out a tech multiple times, but of course always when he comes out it works perfectly fine because it's an intermittent issue. I've even had a tech from Mutoh Australia come out, and they both basically couldn't find any issue and effectively told me "Do a Little Charge as much as required" if that's what you need to do. They basically just blamed the third party ink that's not OEM Mutoh (which isn't even sold in Australia...) and that's that. They don't really seem to be too invested in sorting the issue, but it's really killing me in stopping me print some days.

Recently, my third party ink supplier became an official Mutoh dealer and I've ordered a second machine from them for redundancy, and the fact they can't blame the ink like the original supplier / Mutoh. Then I'll have two identical machines side by the side, with the same hardware and ink that I can compare and definitively say it's the ink or the machine.

In the last few days, I actually did a CR Maintenance straight after a clean and noticed that there are air bubbles in the Maintenance Station and noticed that there were air bubbles on the head too (Presumably, it picks up the air bubbles from the MS, then they work their way into the head) which slowly disappeared when I was watching them during the maintenance as they worked their way into the head. I'm not sure these are related at the moment, but will do CR Maintenance after cleans soon to work out if they are.

Had anyone had a similar issue and know a fix for it? It's painful not being able to print rolls when I'm busy (anywhere from 5-13 customer jobs on each roll) and I'm wasting A LOT of time clearing it up every day. I'm also worried about how many Little Charges that I'm doing.

Thanks in advance,
Alex

 

[unmateria]

Hi Alex... It can be some things... First, the printhead life is between 3 and 6km2... I never seen a dx7 print more than that in 10 years. They begin doing things like this, mixing colours etc... But I think we can expect more life in sublimation ink if not many cleans and those charges has been done. Charges are not a normal procedure... The "eat" printhead life and lots of ink. If after a ink charge it doesnt print, dont keep doing that.

First replace the complete cleaning station if u still didnt do that, or check both tubes from the pump to the station. Make sure that if u inject cleaning fluid from each one, it appears on the cap (with the printhead outside the cap of course).

Replace the wiper. It shouldnt be drops on the printhead after a cleaning.

Replace both black dampers with good ones, or check the rubber seals in the top and bottom. They must be soft rubber, not hard, and the hole should be little and tight, not a big hole. You must feel pressure when inserting pins.

Check the cartdrige rubber too. The one where the plotter needle pinch the cartdridge. The same... It has to be perfect and the cartdridge shount spit much ink from there when taking into your hand... They sometimes get hard and air enters there.

Check the y tubing from the tubes to the dampers and seal them with ink. Let cure the ink all the night.

And the most important because its very normal... Check the orings inside the nuts on top of the dampers. They must be perfect rounded like a donut. Replace them if not, and install them wetting with ink and leave them all the night before trying a charge.

If all is correct... Do one test please... Remove black damper from printhead (be extremely careful with cables... Extremely...) and suck with a syringe and a Y tubing slowly from both holes until you film both chambers... Remove syringe and leave it there hanging all the night... There is air in tubing after all night without doing anything?

 

[Solventinkjet]

I agree with everything above. Sounds like you've got some worn out seals and air leaks.

But I think we can expect more life in sublimation ink

I always thought this as well because dye sub is water based but I actually see the opposite. I'm not sure what it is about dye sub inks but they seem to eat up heads faster than the solvent inks. I'm sue it highly depends on the brand and quality of ink but I have some customers who go through multiple head per year with their dye sub inks.

 

[alexcim]

Thanks for both responses, they're excellent. Where do you both think I should start chasing this, in order of easiest to hardest / cheapest to most expensive.

The annoying thing is that this issue has been presenting basically since I bought the machine. It was first inked up in mid April, and this issue has been happening on/off since May (when first reported to the Dealer).

The current known facts are:
- The issue is that air finds its way into the head
- When the machine is printing, there are no issues with black dropping out during the print (It has happened once, but that's 1 out of 50 100m rolls printed to date, so I'd say that's an outlier). It's very solid when printing.
- Always after a print, I can get a great nozzle check if I do one when a print finishes
- Short prints don't seem to result in the issue after a print (10-15m). I've only ever done 10-20m prints, or 70-90m prints.
- I did short some prints on high ink load too (400 vs 250 normally) and they don't cause the issue after either
- The issue only presents after a 70/90m print, under light vacuum (short, normal, long cleans)
- Once the cleans start, there often doesn't seem to be much chance of going wrong. I mean, it's generally the first clean after a print that introduces air, and from there, cleans are very unlikely to introduce more air - but don't help much to remove it, but do work.
- A strong vacuum (Little Charge) seems to clear up the issue in most circumstances
- Mainly the issue is with the K channels (outside of heads) on the heads, but presents sometimes on the Y, but that often clears with just one or two cleans
- Cyan and Magenta do not present the issue
- The ink supply is shared in the carriage by the same channels on the heads (Left K head 1 Y connects to Left K head 2, etc)

I doubt anything is getting in from the ink supply as I have Bottle -> Bulk Feed Subtank -> Cartridge -> Machine Subtank -> Ink Lines -> Dampers -> Head. This is because:
- Just one clean would not be enough to draw in air from the rear of the machine
- The highest I've ever seen air in the lines is just going up above the heads into the Y in the carriage

What are your thoughts on my conclusion thus far that I am 99% sure the air leak is in the maintenance station area? My feeling is that after a print. one head is sealing well (and it jumps around which one that is), and the other isn't, and when the clean draws ink down via the pumps, it creates negative pressure in the opposite head, drawing air up. The most affected channels are black (and sometimes yellow), because they're on the left/right most boundaries of the seal.

And I am thinking that because it's linked to happening only after a long print, maybe the rubber seal on the maintenance station is drying out which results in a lesser quality seal, or just micro surface imperfections (maybe some dried ink) allowing for air to pass in?

Thoughts?

This is really the only thing I can conclude by linking together long print + air leak.

 

[unmateria]

I agree with you (both)... I dont know that machine, but... can you swap cleaning station? (Would be great to check what you said)

If not, do what i said before, remove the dampers carefully (leaving them connected to the ink tubes). Charge them with a syringe (be careful to not stretch the seals), and leave them al the night there. If at morning ink have returned to the cartdridge, is not a problem on printhead or cleaning station, and you will have do what i said before (checking seals, orings, wet them, etc).

 

[unmateria]

Hi Alex, i have seen the pump... Dont look more, of course its what you said. One cap is sucking while the other dont so it get air on the print and little maybe on damper if its so used (replace them anyway if they have 6000m2)

 

[heyskull]

I had something similar on a machine I was trying to reinstate.
Turned out to be a cracked manifold on the printhead.
When I had a closer look they all crumbled.

SC