SC-540 weird nozzle test failure

[kffernandez]

hi all,

i have an sc-540 with a really weird nozzle test for black. the first pass it prints is consistently fine. while the second pass would have nozzle drop outs. i have attached a few nozzle test for you to see for yourself.

the head in is only a few months old. no head strikes yet. i am using third party inks, but others with the same machine don't have this problem after 2 years of use. dampers are new, ink lines appear to be clear, and i am able to suck ink from the bottom. i manually cleaned the heads twice just to make sure.

for some strange reason, performing repetitive cleanings, medium cleans, and suctioning ink from the bottom just makes the second pass worst.

printing in low carriage speeds [400mm/s] produces acceptable results, while printing at around 600-700mm/s shows noticeable banding.

my gut tells me that this is an ink starvation problem. but from my experience, that would only show itself during printing of heavy or solid colors. not during nozzle tests.

i would really appreciate it if anybody has experienced something like this, and is willing to help.

thanks!

 

[artbot]

it's not uncommon for tests to make the head worse. if you have a big piece of crud in your head the cleaning cycles can simply just be pulling/jamming the clog in worse.

looks like you'll at least need to do a head soak. also, you can fill a damper with cleaning fluid. put a nail or something in the inlet so it won't leak on your print head. then fit the damper on to your black head adapter nipple. this will get cleaning fluid directly to the source. do this a couple of times.

and it's definitely starvation. the head is not starved for ink the second it leaves the park position.

 

[kffernandez]

artbot, just the guy i was hoping to chime in...

here's a follow up question just for you. since you did mention soaking and using cleaning fluids: are all cleaning fluids the same? i mean the distributors around here are selling cleaning solutions like it was a generic thing [some are even interchanging solvent and eco-solvent cleaning solutions]. some are more expensive than others.. and none are saying whether it can be used for flushing or just soaking and cleaning. BUT more importantly, can i destroy my dx4 head if i put in an inappropriate type of cleaning solution?

placing cleaning solutions on the dampers directly makes perfect sense. with your inputs, i now have a feeling that the clog is not on the nozzles. but rather, somewhere between the nipple and the actual nozzles.

thanks again!

 

[artbot]

i've put as strong as 1:1 acetone/butyl cellosolve in a head attempting to get a diverted nozzle clean and the head was none the wiser

(and btw. the head clog did not come out with that mix. so if you think dropping a "safe" chemical h-bomb inside a head is your answer...not always). inks need time to dissolve. long exposure to a weak solvent is better than short exposure to a strong one.) that said...

most cleaning solutions are 1:6ish. the entire system from my experiments (mimaki) is immune to ketones (pure ketones, don't use lacquer thinner, no two lacquer thinners are made of the same thing). i even have MEK as one of the components in a clear solvent ink i make.

as far as chemical difference between eco and full solvent just make sure to do some tests on a piece of aluminum foil mixing the two. look for coagulation. you want to see the ink melt if dry and disperse evenly. or if wet blend and not gather.

but as for chemical differences, i've not yet seen different chemicals for each. the same chemicals keep popping up. just test before using.

 

[kffernandez]

ahh. so, there is basically no danger of the head getting physically corroded or physically damaged by the cleaner chemicals themselves.

if i understand you correctly, the primary danger is with the chemicals reacting with the ink causing coagulation. thus destroying the head. this, which can easily be avoided by just adequately testing the solvents first.

thanks artbot! your tips are invaluable. [ok, maybe as much as the price of a new head]

 

[artbot]

thanks, and as far as your pic. as long as the bad patterns are moving around differently, the head's still cleanable. when that pattern never changes, that is when you've really got a problem.

 

[signimaging]

Did you happen to flush the head with cleaner? some times if you flush the head to hard it will damage the head causing that problem.

 

[Large Format]

To be honest all of your heads look like crap, deflection deflection deflection. It looks like you have swollen head caps. I would replace all of you head caps. Some third part inks can cause this problem

 

[kffernandez]

Did you happen to flush the head with cleaner? some times if you flush the head to hard it will damage the head causing that problem.

actually, i have damaged a head before by suctioning too hard. that's why i haven't been doing that lately. and if ever i do, i make it a point to be very very gentle.

to answer your question... no, i didn't flush the head recently. the last time i flushed this head was about 3 months ago. but it is at the back of my mind that manual suctioning might weaken the head, thus shortening its life. i can't get out of my mind the warning in the manual when it stated that power cleaning [forcing ink through the head] will shorten the life of the head.

 

[kffernandez]

To be honest all of your heads look like crap, deflection deflection deflection. It looks like you have swollen head caps. I would replace all of you head caps. Some third part inks can cause this problem

ahhh.. i knew somebody would point that out. my pic is the one mainly at fault there. in reality, the only one with really bad deflections is my black head. the cyan is almost perfect, magenta has a few as well tho. [5-8]

i have actually replaced all my head caps already. it hasn't improved since then, but neither has it gotten worse. i think the deflections happened when i still didn't know that i had to do make it do its daily cleanings, along with the other list of stuff that we have to do to take proper care of our machines. [i got my machine second hand] i currently can live with the quality of my prints. but if you have tips on how to fix my deflections. i am all ears. btw, i have tried manual suctioning through the cap tops, and head soaks through the cap tops as well. neither improved the quality.

thanks for helping.

kelly

 

[Large Format]

Look at the how the caps align with the heads. If the caps are off center this might be a problem.What is your head hight position?

 

[P Wagner]

...

 

[kffernandez]

Look at the how the caps align with the heads. If the caps are off center this might be a problem.What is your head hight position?

yep. i aligned the heads as well already. the first few weeks worth of nightmares after getting the machine were caused by an unaligned carriage. which as you would expect, dried out my heads every single day. hehe. i now regularly check for a vacuum by testing the heads one by one using a syringe every week or so.

head height is set permanently at middle.

 

[bmendes]

Greetings,
These print heads have a coating on the bottom of them to make then repellent to the ink, once this coating starts to fail generally due to excessive rubbing/cleaning of the nozzle area or strong cleaning fluids you can get similar results to your test image. The first pass of the test print is ok but the next pass is poor. When you print does the banding get worse the more it prints?. An easy way to tell is to print something that is banding and lift the cover so the print head stops midway, look under the print carriage at the nozzle area an see if there are any droplets of ink on the nozzle area. Also the hight of the wipers may be set too low causing the head to not be wiped clean before printing. Do a light clean and test print with the head in the Low position - Remember to slide the media clamps down to the left hand side before you do a test print with the head in the low position. last possible cause that i can think of is a crack in the nipple that the damper attaches to, this prevents the head refilling with ink or lets air into the head itself

Hope one of these suggestions help
regards
Brett

 

[kffernandez]

Greetings,
These print heads have a coating on the bottom of them to make then repellent to the ink, once this coating starts to fail generally due to excessive rubbing/cleaning of the nozzle area or strong cleaning fluids you can get similar results to your test image.

i didn't know there was such a thing. but it does make sense. for about a month or so before, i was a bit paranoid, and left the heads soaking in their caps with cleaning solution continuously. afterwards, i felt that nobody else was doing it... so, i stopped. that could have stripped away that coating that you mentioned. is there any way at all to regain that coating? it would be such a terrible waste to discard a head just because the repellant coating wore off. :Oops:

the banding is weird. aside from an overspray around the edges, the banding seems to look like alternating bands of light/dark horizontal shades. of course, the bands get thinner as resolution increases.

a few other clues to include here is that (1) i tried swapping the black dampers with the cyan dampers. and it obviously improved the results from the offending head. there were still a few missing nozzles. but it was definitely an improvement. and (2) i have replaced the head nipples, and it hasn't changed the results. (3) the wipers are definitely doing their jobs. i have looked at the heads after cleaning, and their bottoms are spotless.

i will try stopping the carriage during print to see if droplets are forming, and get back to you.

thanks for the input!


kelly