White UV Ink Issues - From bottle to print head

[mkp007]

I have a cheapo UV flatbed printer that is based on the Epson 7880 and the DX5 printhead. CMYK+WWWW. I have had good success but this always comes with hours of frustration. Many issues, and most of them stem from the UV white ink.

If you know the 7880, it has the 4 ink cartridges on the left and 4 on the right. My machine has 8 bottles of ink with a ink line to each (4 lines to a larger white bottle). There are no fancy seals on these bottles so one question that has bothered me was "how are these bottles different from the ink cartridge in terms of ink delivery?". If the printer is left idle for 2 hours, I need to reprime the print head. I do this by sucking a bunch of ink through the print head. How? I hook up a vacuum pump to the waste line and pull 20in Hg for about 60 seconds. This wastes about 30-50ml of ink. I actually installed a valve on each line so that I can shut off ink lines if one channel is bad to save ink.

I can't figure out why I need to do this? I really don't think the ink dries and clogges the print head. My best guess is ink is draining away from the print head back into the bottle. This is actually why I installed the valves in the first place; however, I don't notice much difference when I shut off all the lines after using the printer and then coming back to it after a few hours. I still have to prime it. And it does it to the color just as easily as the white inks. The bottles are just slightly lower than the print head. I was wondering if I raised them to be 12in above the print head if ink would drain (siphon) out of the print head? Or does the print head nozzles seal off when not powered?

there is a lot more to this but I think I will just stop here and see if anyone has any input on this particular issue.

thank you in advance for your input.

 

[rubo]

get rid of bottles - get refillable carts and chip resetter - had that setup for years never had any issues - printer would stay idle for 3-4 days at a time, would go right back - maybe a nozzle check once in a while to keep the "blood" flowing. all w pigment inks.

 

[artbot]

the white ink is heavier and has more surface energy than the other colors. so while the cmyk is flowing down the tube and easily stretches under the gravity pulling it toward the head, the white is more resistant to stretch and is like a bungy cord and pulling itself back toward the greater/heavy side of the ink train. i'd first try raising the ink bottle just a bit. this may do nothing because it's probably hooked to a cartridge which might cancel out the raising. if it were me, i'd first get rid of the white ink bottle and move to four standard black carts for the white ink. i'd keep these carts full to the top and i'd give them an aggressive shake before needing to use them. also, flush the white ink lines. it's very possible that you've got a great deal of sediment at the bottom of these lines. one problem with that is if there is sediment, solvent will have no effect on it. the white ink is simply crushed calcium carbonate and will plaque up the bottom of your ink lines. if this is the case, you should change your white ink lines out and use the next size up for the ink line. if you don't have a recirculating system on a white ink printer, you can not keep white ink in the lines for over a day without printing. it's the nature of the ink. i had white ink on my old jv3 and i opted for a single ink line that split to several dampers at the head. this allowed for much simpler maintenance. i would reverse flush the white ink line as soon as i was done with printing. this was because i would print white ink about three times a month, all day then the printer would not use white ink for a week or two.

 

[mkp007]

It's not just white.

... i opted for a single ink line that split to several dampers at the head. this allowed for much simpler maintenance. i would reverse flush the white ink line as soon as i was done with printing. this was because i would print white ink about three times a month, all day then the printer would not use white ink for a week or two.

Artbot, I agree with this and I will probably do this modification when I change the ink lines.


Thank you for the replies, but please recall from my post that CMYK is just as problematic as the whites. Just as we speak, I have been trying to get black to prime (black and yellow for some reason are more of a problem than cyan and magenta). Right now, the ink in the bottle is about 4 inches lower than the print head. I'm going to raise the bottles up by 5 inches and see if this changes anything.

This is just one issue I'm having and I believe it is independent of color. I started this thread with white in mind but as I was writing, I decided to focus on this issue first.

Bottle vs cartridge is very interesting to me. What does the cartridge do that makes it special? Does it keep ink from moving backward like a diode does with current? I have a stock Epson 7880 (stock version with normal ink) and clear refillable cartridges. There seems to be a vacuum inside the cartridge as the fill cap is being sucked down to the carriage. It is important for some reason to raise the ink lever and remove the cartridge prior to taking off the fill cap. I accidentally took off the fill cap while in the printer slot and this caused a temporary issue that I resolved by running a head cleaning. So, having negative pressure in the ink cartridge is common and is something that is missing from my setup with the bottles (bottles have no seal). Any thoughts on how this could help keep ink in the print head?

Thanks again.

Mark

 

[artbot]

the cartridge can come in many designs. you can see in the clear refillables that they have "downhill" interior to keep ink feeding to one end. these printers are referred to as "gravity feed". think of the ink train as having a heavy and light side. if you were to hang a heavy chain off the edge of a roof one link at at time, eventually the weight of the links hanging off would pull the rest of the chain off link by link rapidly. your ink is that chain held together by surface tension. the cartridge is the heavy side (pile of chain on the roof) the ink lines are the part of the chain hanging off the roof. raising the carts will put more downhill pressure in the lines by increased gravity.

(if you get air in your lines, you break the chain and the ink drifts backwards to the heavy side) if you are losing ink in several channels then you have to figure out if you have a weight issue, clog issue, air leaking near the head carriage, etc. the damper is there to hold the ink at the end of the ink line, if air is getting in there or at the head manifold your ink will travel back.

i'd bet that the uv ink is slightly heavier than the standard ink and needs more encouragement to stay at the head. i'd experiment to get as much weight pushing down the lines as possible. i'm not sure if raising the ink bottle will do this in that the cart' may cancel this out.

 

[mkp007]

How the Epson 7880 Cartridge works

....the clear refillables that they have "downhill" interior to keep ink feeding to one end. these printers are referred to as "gravity feed"... ....i'm not sure if raising the ink bottle will do this in that the cart' may cancel this out.

This is important so I will dwell into it some more. Attached is a photo of my Epson 7880 refillable cartridge. The exit port sits approximately 6 inches lower than the print head. So, ink has to travel up vertically a net of 6 inches. I think this negates the gravity feed theory. The ink lines go from the cartridge directly to the print head (I think, I can't tell if there is something special the cartridge engages into). There is an ink pump that is attached to the capping station. So, the ink is pumped from the cartridge, through the ink line, to the dampers, through the print head, into the capping station, through the ink pump and into the waste bin (i.e. maintenance tank). It seems to me that the print head itself draws the ink from the cartridge (ie the print head is a pump when purged with ink). When the print head is not firing, it is a tiny open valve (I think). Inspecting the ink cartridge, you can see a ball valve that opens when the cartridge is inserted into the holder. Is there something other than a line there?

Page 8, assembly 668 in lower left. see manual here: http://www.gedat-spareparts.com/ex/stylpro_7880.pdf

part list here: http://www.gedat-spareparts.com/epson/Inkjet_Printers/STYLUS_PRO_7880/list

 

[artbot]

there's not gravity "theory" about how the ink gets to the head. the head does have a micro pumping action in the piezo but that fires the ink that then pulls the ink train through it at the platen.