Luminous Landscape Forum
Raw & Post Processing, Printing => Printing: Printers, Papers and Inks => Topic started by: cybis on August 22, 2015, 01:11:57 am
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Not sure if this applies to printers other than the Epson 7/9900, and not sure if ink sedimentation is a real or imaginary problem, but I had this thought while thinking about John’s missing channels problem (http://forum.luminous-landscape.com/index.php?topic=103164.0):
Epson recommends agitating cartridges before installing them; therefore we can safely assume that ink sedimentation can occur. But what to do once the cartridges are installed: to shake or not to shake, that is the question. Whether ‘tis Nobler the carts to agitate.
One idea being floated around is that there is no need to regularly remove and agitate ink cartridges: in the normal process of operating the printer, the ink inside the cartridges will be sufficiently mixed by the pressurization cycles squeezing and releasing the ink bags inside the cartridges.
But how could this work? There shouldn’t be any air mixed with the ink, and the ink, being liquid, doesn’t change volume with pressure changes. None of the components exposed to pressurized ink on the inside and ambient air pressure on the outside are flexible enough to expand significantly under operating conditions. Therefore the ink bags don’t change shape during pressurization cycles, and no mixing of the inks should occur. The ink bags do very slowly change shape over time as ink is being consumed, but this won't be sufficient to mix the inks.
Maybe some of us have been misled (or at least I have) by the sound coming from the carts during pressurization cycles, which seems to be the sound of ink bags changing shape, but is actually from the membrane sealing the air chamber inside the cartridges. The membrane is being pushed against the inside of the cartridge and makes a sound as it expands and contracts.
Relying on pressurization cycles as a way to agitate the ink and prevent ink sedimentation without removing the cartridges and manually agitating them, is probably not a working solution.
If ink sedimentation does actually occur, and if the denser part of that mixture contains a greater fraction of pigments, and if higher pigment concentration tends to cause more nozzle clogging, then such clogging would tend to appear when ink from old, unagitated, almost empty cartridges reaches the printhead.
It takes a long time for ink to travel from a cartridge to the head. So clogs would tend to show up very many prints after such ‘bad’ ink first enters the ink lines and potentially very many prints after replacing old cartridges with fresh ones. The long time delay between the cause and the symptoms would mask the causality link to the user.
More clogs, means more cleanings, and if cleanings shorten the lifespan of x900 printheads, not agitating cartridges in low volume environments could be another factor in x900 printhead failures, as it has been suggested by others in the past.
Is there any evidence of that happening?
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Yes, I never imagined agitation happening by the air pressure system Epson uses. Carts also are inserted horizontally with the seal halfway in height at a vertical side so if there is pigment settling it happens in the lower half of the bag and that ink will be used at the end of the cartridge's life if not shaken periodically. Very passive way of applying pressure on the system.
On the other hand modern pigment inks stay in suspension very well. The pigment particle coatings have special characteristics for that purpose. One way to test pigment settling is using a (DIY) centrifuge like Paul Roark has done to test his quad ink mixes.
Actual ink agitation in the carts happens in my opinion in the HP system used on many of its printers, not just the Z models. I took the bag out of an empty HP cart and cut the top of that bag off. Cleaned most ink out. Filled with water. Syringe needle in the seal, pushed the rubber ball = membrane pump with a pencil and water went through the syringe needle. Nothing unexpected so far. Then I removed the syringe needle. Did the activation of the pump. Looking inside the bag I saw remaining ink from the pump section flowed in and out of the pump section and the bag. This and the more or less vertical position of the carts and seal + pump beneath suggests to me that ink agitation happens in the HP carts. I was already wondering about the fact that all pumps or at least 6 cart pumps at one side are activated when there is an ink request, the actuators of the pumps are driven by a kind of camshaft driven by one electric motor so all rubber balls are pushed in, one after the other. Actual ink flow is controlled by the butterfly valves in the head ink buffers, with buffer full there is no ink flow = ink agitation. The periodic cleaning also comes with the sound of pumps being activated, kind of high pitch sound like a leather or rubber belt slipping on a drive wheel.
There are more ways to keep inks agitated, white and metal color inks are known to have fast pigment settling. By pumping inks through a tubes loop, ink ending in the cart again and the heads halfway that loop, the inks remain in agitation over the entire channel. Heavier tube assembly of course. For normal inks the sideways movement of the tubes should already agitate the ink in the tubes. In all inkjet heads there are special compensations in the ink channel structure to overcome influences of the head carriage movement, sideways acceleration-deceleration, on nozzle ink supply pressure, indicating agitation there.
Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots
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I have a 3880, so my observations may or may not be applicable to the larger Epson printers.
I recently had a PK black cartridge run out 1/2 way through a print of a night time image with a jet black sky. The ink cartridge had never been taken out and agitated other than when it was installed and other than the normal slight jiggling that the printer does while printing. I replaced the PK black cartridge with a new one which was gently shaken for about 20 seconds. When I examined the print, there was no difference what so ever in the blackness of the sky, but there was a difference in the amount of gloss. If one looked carefully at the print surface reflection you could identify exactly where the cartridges were swapped.
So I don't know about the pigment settling in the cartridge, but there may be other things that may vary between the beginning and the end of the cartridge.
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Jay, that's an interesting observation. I have no experience with that printer, but I guess on a 3880, you were able to observe the effect of a cartridge swap instantaneously. How soon after the print came out of the printer did you observe the difference?
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Ernst, it's very cool to have your insight into the various technologies out there. Epson definitely seems to be lagging behind HP in that area. I wonder how the Canon LFP deal with the issue.
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When I examined the print, there was no difference what so ever in the blackness of the sky, but there was a difference in the amount of gloss. If one looked carefully at the print surface reflection you could identify exactly where the cartridges were swapped.
I haven't had this happen to me, so I have no experience to draw on. But surely what you're seeing isn't the new ink, is it? The 3880 has a fair bit of ink in the ink lines and dampers. and it's going to take some time for the ink in the new cart to make its way to the print head and onto the paper. Isn't there something like 15ml in each ink line? I'd be interested to know what caused what you're seeing, but if I'm right in what I say then it can't be different levels of ink agitation and pigment suspension. Not so quickly.
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I haven't had this happen to me, so I have no experience to draw on. But surely what you're seeing isn't the new ink, is it? The 3880 has a fair bit of ink in the ink lines and dampers. and it's going to take some time for the ink in the new cart to make its way to the print head and onto the paper. Isn't there something like 15ml in each ink line? I'd be interested to know what caused what you're seeing, but if I'm right in what I say then it can't be different levels of ink agitation and pigment suspension. Not so quickly.
Right, I wouldn't expect that either. I wonder more whether the end of the old cartridge influenced the ink amount applied versus that of the full new cartridge on the PK channel.
Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots
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That's a good point. In retrospect, I couldn't tell exactly where the ink ran out because that part of the image was still inside the printer. It was only some time later when I picked up the print that I had set aside to dry that I saw an abrupt boundary in the amount of gloss.
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Jay, is there any chance at all that what you've observed was simply the ink on part of the print having had a chance to dry at lot longer that the other part of the print? Was the difference still visible a day later?
If the difference wasn't due to differential drying, then Ernst is on to something when he says the difference may be due to a change in the amount of ink. Maybe an almost empty ink bag behave like an almost empty toothpaste tube: it's hard to get to the last bits.
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Here is another thought (not an explanation for Jay's observation): maybe when ink sits too long, it's not really the pigments that settles but the chemicals. I wonder if the water - glycol - glycerol solution can separate over time (any chemist out there?). If this is the case, those chemical have different viscosity and surface tension properties that may affect how ink behaves in the printhead.
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I have located the print, (it was printed last winter and discarded), there is still a band about 2 cm wide that looks a bit different. It was printed on Han Fine Art pearl so the gloss differential is not so apparent when I look at it now. I don't have an explanation for it, but that band hasn't appeared on other prints of the same image.
The lesson to take away from it is don't let your ink run out!
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I have located the print, (it was printed last winter and discarded), there is still a band about 2 cm wide that looks a bit different. It was printed on Han Fine Art pearl so the gloss differential is not so apparent when I look at it now. I don't have an explanation for it, but that band hasn't appeared on other prints of the same image.
The lesson to take away from it is don't let your ink run out!
Cybis' explanation that the ink had time to dry at that band before the printing was continued is more plausible. Just part of the ink droplets weaving happened at the band and was continued after the cart exchange, the absorption by the inkjet coating in two steps and each step with half the normal ink layer (more or less) makes a difference to the laying down of the total amount of ink within some seconds. Gloss difference is easily created if I see the difference between Economy and total sheet Gloss Enhancer applied on my Z printers, the total sheet mode lays down more GE and some papers (for example Epson Proofing White Semi Matte) show a dramatic gloss difference between the two modes.
Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots
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Jon Cone mentions agitating the carts every two weeks here: http://www.inkjetmall.com/tech/content.php?133-Printer-Cleaning-and-Preventative-Maintenance&s=949279a4dffe258e01ee28a53a016f8d (http://www.inkjetmall.com/tech/content.php?133-Printer-Cleaning-and-Preventative-Maintenance&s=949279a4dffe258e01ee28a53a016f8d)
"Agitate ink cartridges every 1-2 weeks to maintain in-suspension pigment, and use printers at least once a week to avoid settled ink in the pro model internal ink lines and to keep the print head moist."
I have seen "Ring around the cart" where some ink has left a tell-tale bit of pigment on the walls of the refill carts and some refill bottles. Often with the bottles I can dissolve it back into solution with a lot of shaking.
As for the gloss differential of the OP's black, that can be due to the thinner in the ink, and also how much of it is being sprayed out of the head. Spray to much and it can reverse in the density value easily in the black region. I use QTR (A RIP software) sometimes and one can control the ink densities with it, but if I go too much to make it blacker, the outcome may actually be a lighter black which seems wrong, but too much and it begins to dull in appearance - and the spectrometer sees it too.
Over time printing with the same carts, I have seen a profile change between a new cart and once they get towards being empty; i.e. Reading a new cart vs. old cart test print. Dunno. Sometimes I've had nozzles clog midway through printing too which is more maddening and maybe an air bubble or something.
When I delved into that expensive Piezography B&W stuff, the entire first run of that ink was a costly "flush ink." The former Yellow cart had a very light shade of black ink and on occasion it would show a yellow tint in the light black areas of an image. Same for one of the Magenta inks. Really became a crap shoot in trying to match something. Sometimes some small crevice was holding some of the old colored stuff and it just got loose. The second round of ink helped a lot, but I wasn't too crazy about spending $450 for an initial "flush ink." Still not that crazy about that system either as some papers have their own tint and there were times when I'd like my tint to be different than a fixed tint off the Pizeography ink set. Also, too much gloss differential on glossy papers that was not addressed by their "Gloss Optimizer" second-pass printing. So back to Adobe RGB printing and away from the fixed-tint of the Gamma 2.2 piezo stuff.
SG
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Regarding the issue of water - glycol - glycerol - pigment separation, I did a quick search:
- Water and glycol are very hard to separate. Doesn't seem likely that gravity would do the work.
- Glycol and polymer nanoparticles won't separate in centrifuges. I don't know what pigment particle coating Epson uses but it seems very likely they've developed a method to prevent glycol - pigment separation. Epson may have solved that problem. Third party ink manufacturers, and DIYers, probably not.
- Glycerol and water does separate easily in centrifuges...
Glycerol is the denser of the three and would settle to the bottom. It also significantly affects the viscosity of the mixture. I wouldn't jump to the conclusion that the higher the viscosity the more nozzles will be missing. In fact, it could be the opposite. I'm currently experimenting with water with a bit of jet dry (in an attempt to match the ink's surface tension) and color dye in my 9900 cartridges. I'm surprised to find that the printer is more prone to exhibit missing nozzles after a period of inactivity than with Epson ink. This seems to confirm missing nozzle are mostly not clogs. Is viscosity the key? This is a bit far fetched but is viscosity too low in high temperature environment somehow leading to more missing nozzles? Ink solution contains about 15% of glycerol. If glycerol does separate to the bottom in low volume - no agitation - high temp environments, for most of the time the printer would be fed with a low glycerol, low viscosity solution.
I see a centrifuge in my near future ;D
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Therefore the ink bags don’t change shape during pressurization cycles, and no mixing of the inks should occur.
The ink bags I do believe change shape, when the printer is off, the ink will settle to the bottom and expand the bottom of the bag out. When the printer is turned on, the bag is squeezed so the ink in the bottom is pushed upwards.
As to whether sedimentation is a problem, I've never seen any evidence of it and no longer remove my cartridges to shake them as I believe that can cause more problems. Shaking new cartridges is recommended because they possibly have been sitting for an extended length of time, but I think the slight vibration of the printer as it moves back and forth plus the pressure changes when turned off and back on are sufficient. It's not like things settle out quickly and easily.
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The ink bags I do believe change shape, when the printer is off, the ink will settle to the bottom and expand the bottom of the bag out. When the printer is turned on, the bag is squeezed so the ink in the bottom is pushed upwards.
As to whether sedimentation is a problem, I've never seen any evidence of it and no longer remove my cartridges to shake them as I believe that can cause more problems. Shaking new cartridges is recommended because they possibly have been sitting for an extended length of time, but I think the slight vibration of the printer as it moves back and forth plus the pressure changes when turned off and back on are sufficient. It's not like things settle out quickly and easily.
Wayne, I think physics makes it unlikely that the ink bag could change shape the way you described it. After your post I tested this by pressurizing a cartridge with the cover removed and observed that indeed the ink bag inside did not change shape whatsoever.
Here is the link to the video of my test: https://youtu.be/_irPncMwIbc (https://youtu.be/_irPncMwIbc)
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Cybis:
Third party ink settling was a real phenomenon 8-10 years ago. When I quit using third-party bulk inks in an old Epson 9000, I observed yellow pigments obviously settling toward the bottom of a bottle, that had sat undisturbed for a year. Ink formulation has steadily improved, and the new co-solvents and pigment encapsulation have greatly improved. But it is still wise to not buy ink carts larger than what you might use up within a year. As much of a problem with pigments, is the coagulation of pigments into larger particles. In any event, just shaking the cart on a periodic basis will not really do much to help prevent either of these conditions. The best solution is to use fresh ink. FYI, Pigments are more prone to settling and coagulation than dyes.
As Ernst has observed, HP probably has the best system for keeping their inks thoroughly mixed. Also, HP grey inks are created with a consistent color balance. When you print in grey and black only mode, no color pigments are used to neutralize the warmth of carbon black. HP uses a lot of grey component replacement--evidenced by the much greater usage of especially light grey and grey inks. This probably explains why fade tests consistently show a linear fade and 100-200 print life unlike Epson or Canon.
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Jon Cone mentions agitating the carts every two weeks here: http://www.inkjetmall.com/tech/content.php?133-Printer-Cleaning-and-Preventative-Maintenance&s=949279a4dffe258e01ee28a53a016f8d (http://www.inkjetmall.com/tech/content.php?133-Printer-Cleaning-and-Preventative-Maintenance&s=949279a4dffe258e01ee28a53a016f8d)
"Agitate ink cartridges every 1-2 weeks to maintain in-suspension pigment, and use printers at least once a week to avoid settled ink in the pro model internal ink lines and to keep the print head moist."
I have seen "Ring around the cart" where some ink has left a tell-tale bit of pigment on the walls of the refill carts and some refill bottles. Often with the bottles I can dissolve it back into solution with a lot of shaking.
One of the challenges in using non-OEM inks, color or B&W, is sedimentation. So that's one of the cost-benefit trade-offs you make when you elect to go that route in a Pro printer. Hence Cone's reported instructions for his inks. The general consensus here on Lula is that it's not much of an issue for OEM, and that's my experience as well.
As for the gloss differential of the OP's black, that can be due to the thinner in the ink, and also how much of it is being sprayed out of the head. Spray to much and it can reverse in the density value easily in the black region. I use QTR (A RIP software) sometimes and one can control the ink densities with it, but if I go too much to make it blacker, the outcome may actually be a lighter black which seems wrong, but too much and it begins to dull in appearance - and the spectrometer sees it too.
Over time printing with the same carts, I have seen a profile change between a new cart and once they get towards being empty; i.e. Reading a new cart vs. old cart test print. Dunno. Sometimes I've had nozzles clog midway through printing too which is more maddening and maybe an air bubble or something.
The OP had a specific problem, which was changing a cart mid-print left a band which could be seen as having a gloss differential but not a density differential. I can't see how any of this relates to his specific problem. There's no way that the ink from the new cart could have made it to the print so quickly and as the changeover only took minutes, I can't see that anything could have happened in the ink lines either. You'd see that as a density differential.
I think Ernst's explanation in his last post is on the money. The brief pause in printing meant that the two step absorption produced a differential gloss to the rest of the print which has a one step absorption. Which is unlucky. I thought you were supposed to be able to change carts mid-print in a Pro printer. I wonder if this only visible in such a large dark area like a night sky.
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The OP had a specific problem, which was changing a cart mid-print left a band which could be seen as having a gloss differential but not a density differential. I can't see how any of this relates to his specific problem.
There might be a little bit of confusion here. The OP (me) is interested in discussing ink settling and how it might relate to missing nozzles and/or impact the printing process in a very general and broad way, but with an eye on the Epson x900 printhead issues.
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There might be a little bit of confusion here.
You're right, there certainly was. I forgot the original question and thought it was Jay's post. My apologies to you and SG.
My experience is that sedimentation is an issue with 3rd party inks, but I've never found it to be a problem with OEM. But then I've never had an x900 printer.
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Ferp, no worries; I'm not quite sure where I'm going with this myself ;)
Just for fun, here is a quick and dirty video of the piezo capillaries filling up with cleaning solution under a microscope: https://youtu.be/pq3OH6iFc-8 (https://youtu.be/pq3OH6iFc-8)
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Wayne, I think physics makes it unlikely that the ink bag could change shape the way you described it. After your post I tested this by pressurizing a cartridge with the cover removed and observed that indeed the ink bag inside did not change shape whatsoever.
Here is the link to the video of my test: https://youtu.be/_irPncMwIbc (https://youtu.be/_irPncMwIbc)
Right, expected that but I have not tested it like you did and made convincingly visible, thank you. Based on several dissections of Epson carts and simple physical laws I did a brain animation yesterday of the typical Epson cart with pressure applied around the ink bladder and without. No air gets into the ink bladder without ink pressure applied so no compression of air or other gasses happens inside the bag, liquids are not compressed at that kind of pressure levels so no volume change happens, the small bulge of ink in the underside of the bladder is created by gravity and that does not change between the two stages. I can imagine PET bag material folds that readjust at some stage of the bag draining when air pressure is applied but that would be a minor stir for the ink content. I have seen some different ways of bag construction/folding/welding over the last decade and most constructions aim to make the bladder flat without interrupts when emptied, often by gluing one side partly to a vertical wall of the cart. Especially by gravity fed ink systems the bladder has to keep a constant feeding without gravity pressure changes, hence the ink outlet halfway the height and the bag flattening sideways and not dropping to the bottom of the cart.
My son yesterday gave a link to a more hilarious scientific exposé on volumes where within little agitation happens:
https://www.youtube.com/watch?v=Wf1pNnoSuQc He intends to be there this year. If I continue writing messages like this I might end up on that stage too and it would not be a waste of time as it is comedy. Edit: even the Hamlet part of the subject line is not overlooked, drama avoided though.
Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots
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I guess makes some sense, most of the air pressure would fill in the empty voids and squeeze the bag as is. I think when the bag is approaching empty it may change shape a little more as the pressure will squeeze the ink towards the port which is in the middle.
But I still believe the motion of the print head and vibration during printing is adequate to keep things suspended unless the printer sits idle for an extended period of time.
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I guess makes some sense, most of the air pressure would fill in the empty voids and squeeze the bag as is. I think when the bag is approaching empty it may change shape a little more as the pressure will squeeze the ink towards the port which is in the middle.
But I still believe the motion of the print head and vibration during printing is adequate to keep things suspended unless the printer sits idle for an extended period of time.
There shouldn't any air in the bag. There is nothing that would change volume under pressure. Nothing that could change shape when exposed to differential pressure. Trust me, it's not happening with the bag full or near empty or anytime. Only gravity, acceleration, vibration, agitation, and ink flow could have a mixing effect. I can't wait to put my hands on a centrifuge to see if it even matters. You are right that the printer motion may be sufficient. I think it all need to be tested.
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;D
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1st result : pigments settle.
2nd result: wife unsettled.
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More preliminary results: in addition to pigment sedimentation, there is some liquid separation.
Edit: this is not a pure ink sample. Pure ink is too opaque to see the layers. This is water plus some green ink. I need to verify the same thing happens in pure ink.
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Here is my own experience with ink sedimentation on an older 7880 machine using Epson K3 inks, in particular the magenta inks seemed to be more prone to sedimenting-clumping, however I think the age of the inks and frequency of use are also important factors in sedimentation.
Please be aware that these images are taken with a phone camera so not real sharp, the ink damper shows extensive sediment and in the magenta ink line you can see seperation of the pigment and binding fluids.
This particular printer sat unused for about 10 months before I received it.
Brian.
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There shouldn't any air in the bag. There is nothing that would change volume under pressure.
I know there is no air in the bag. but the printer pressurizes the space around the bag to squeeze it. since the exit is not at the bottom, some of this action will squeeze the ink upwards toward the port.
More preliminary results: in addition to pigment sedimentation, there is some liquid separation.
Edit: this is not a pure ink sample. Pure ink is too opaque to see the layers. This is water plus some green ink. I need to verify the same thing happens in pure ink.
possibly the ink is just settling out from the extra water?
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some of this action will squeeze the ink upwards toward the port.
No, I don't think so. Imagine a flexible elastic rubber balloon filled with water and no air, tied off at the end so that water cannot escape. Suspend the balloon in a glass jar so that there is plenty of air around it. Now seal the jar and imagine there is a way to vary the pressure inside the jar. You can create a vacuum or increase the pressure at will inside the jar; the balloon will not change shape whatsoever. The liquid inside the balloon or the ink bag doesn't 'know' where the exit is since it is closed. There must be a youtube video of this somewhere; it would be a fun experiment :D
possibly the ink is just settling out from the extra water?
I'm also thinking that's what's going on here, especially since the volume of liquid on top seems to correspond more or less to the amount of ink I added to the water. But on the other hand that's kind of weird as pure Epson ink contains 60 - 65% water. Why would the water I added act differently from the H2O that's already in? I'm no physicist, but I'm even less of a chemist.
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Why would the water I added act differently from the H2O that's already in? I'm no physicist, but I'm even less of a chemist.
Bearing in mind that the original water would be de-ionised.
Brian.
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Bearing in mind that the original water would be de-ionised.
Thanks Brian, I used the water coming out of my RO filter. Should I use distilled water instead? Distilled, deionized, same thing?
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Luc, should be the same thing, not sure if it will make a difference to the centrifuging of the mix though.
Brian.
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Take yellow ink straight, not diluted. Way more convincing. I have seen more pigment settling in yellow ink than in any other ink, possibly because it shows it faster, the density of the ink is low.
Met vriendelijke groet, Ernst
http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
December 2014 update, 700+ inkjet media white spectral plots
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The liquid inside the balloon or the ink bag doesn't 'know' where the exit is since it is closed.
true, until the exit is no longer closed. At some point the pressure is pusing the ink up to the port so it can get out. If the bag is only 25% full, all of the ink will settle and expand the bag out at the bottom, possibly to the point there is little ink near the port. As the pressure is reapplied and the exit opens some movement of ink upwards must occur
I say this for the sake of discussion ... I agree that the changing of the bag shape is probably so minor and gradual as to not be a factor. it's probably a pretty simple gradual collapsing over time.
Why would the water I added act differently from the H2O that's already in? I'm no physicist, but I'm even less of a chemist.
I'm not a chemist either but guessing there is a lot more going on here than simply putting some glycol, water and other stuff in a bucket and stirring it up. There are probably a lot of other agents used, some of which may even be for the very purpose of maintaining the suspension and mix, and just adding water and stirring it up may not achieve a similar "mix".
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true, until the exit is no longer closed. At some point the pressure is using the ink up to the port so it can get out. If the bag is only 25% full, all of the ink will settle and expand the bag out at the bottom, possible to the point there is little ink near the port. As the pressure is reapplied and the exit opens some movement of ink upwards must occur.
I say this for the sake of discussion ... I agree that the changing of the bag shape is probably so minor and gradual as to not be a factor.
Yes, the bag will change shape extremely slowly as ink is being consumed (obviously) but not with the pressurization cycles at all. The port is always exposed to ink (until all the ink is exhausted), ink doesn't need to travel there as it's already there. Although as the cartridge empties, the ratio of ink flow to ink volume in the bag increases, and towards the very end of the cartridge that ratio will be high enough to effectively mix whatever is left of the ink.
I think we now agree that in the absence of ink flow, a pressurization cycle won't make the bag change shape whatsoever, correct?
Now, what happens when ink starts to flow out the bag in a pressurized cartridge? Does the bag then somehow change shape? Yes, proportionately to the ink flow to volume of ink in the bag ratio, i.e. extremely slowly. But this is unrelated to the pressurization feature. The same would happen in a unpressurized system, or even a bag less refillable type cartridge Edit: no mixing from container shape change in a bagless cartridge obviously.
(I'm enjoying this exchange btw :) )
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the ink damper shows extensive sediment and in the magenta ink line you can see seperation of the pigment and binding fluids.
Yikes!
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Cybis:
Remember that centifuging is different than settling from sitting. Centifuging will separate the components according to weight. But centifuging is also different than chromatography, where particle size, and not particle weight is the separating factor. But interesting things you are observing. Carry on!
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Cybis:
Remember that centifuging is different than settling from sitting. Centifuging will separate the components according to weight. But centifuging is also different than chromatography, where particle size, and not particle weight is the separating factor. But interesting things you are observing. Carry on!
Thanks John! Yellow spinning in the machine as I type this (thanks Ernst). My understanding is that the difference between the centrifuge and gravity alone is the ratio of the acceleration force acting on component with various density (Archimedes' principle) to molecular bond forces. In both cases it's a relative density issue but gravity alone might not be able to do the work even on long time scale. So if I'm able to observe separation in the centrifuge, I'll need to compare it to a sample subjected to earth's gravity alone for a long time.
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I'm not a chemist either but guessing there is a lot more going on here than simply putting some glycol, water and other stuff in a bucket and stirring it up. There are probably a lot of other agents used, some of which may even be for the very purpose of maintaining the suspension and mix, and just adding water and stirring it up may not achieve a similar "mix".
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Update on the pure yellow: we have separation. There is a distinct layer on top with a volume of about 7%. Unfortunately, pure yellow is still too opaque to clearly observe what is going on below it. I'll run more tests next week.
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This looks similar to the 3rd party pigmented ink separation I saw 8 years ago from sitting for one year. But mine had a chalky looking upper layer.
But like a wrote before, the thing that the centrifuge won't show is the clumping of the pigment particles. Obviously you would see that type of result in the screen of the damper though!
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...the thing that the centrifuge won't show is the clumping of the pigment particles. Obviously you would see that type of result in the screen of the damper though!
Great, now I need a (stronger) microscope. Thanks John ;)
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I don't know about you guys, but I have been using Epson large format printers for about 12 years and I have always removed my ink carts and gently shaken them from time to time to assure pigment suspension, especially in times when I'm not running a lot of media through it. With the earlier models especially is was really the only way to go.
My opinion is you should always do this regardless of the ink used. If you are in a strict production environment where you are going through several carts every month, the action of the printer is most likely sufficient to keep the ink compounds blended. But letting a printer sit for months with little or no use is inviting disaster, as Ansel Adams was fond of saying.
The only printer that I have ever owned that I would say does not require this is the Canon IPF series. That printer really agitates the carts automatically in a forceful way. Each time you put in a new cart it does it for a long time. Also the carts are facing down and don't require a lot of excess pressure to move the ink into the holding tank and heads. But if the Canon was unplugged and left idle for a length of time even they might need to be manually mixed by shaking the carts by hand, though I doubt it considering how aggressive that auto shaking process is. But I would do it anyway. With the Canon you would probably end up with ink drying in the nozzles and ruining the head before the pigments became unsuspended with the base.
john
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Also, with the Canons, the inks are "push-pulled" in and out of the carts from time to time, according to the service manual.
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While waiting for equipment to arrive in order to test the inks further, I’ve been playing around with the dampers and I think there might be a problem with their design.
The dampers perform three functions:
- 1. Filter the ink. I don’t think the filters are problematic, but on the x900 the filter ‘windows’ are on the downstream side (unlike the filters in Brian’s 7880 picture), so it’s impossible to see if there are particles accumulating there. The filters are also a lot smaller than on the 7880. I reversed the flow of ink over the filter to try to catch any particles in a paper filter but couldn’t see any, which is good.
- 2. Damp the ink pressure. The thing I never realized until now is that the main role of the dampers is not just to damp, but to completely depressurize the ink before it reaches the printhead. The ink reaches the ‘high pressure’ side of the damper at approximately 4.5 psi of differential pressure (approximately 5 psi in the ink cartridges minus .4 drop from the height difference between the cartridges and the dampers). By a system of valve, spring, membrane, and suction, the absolute pressure on the ‘low pressure’ side of the damper is less than the atmospheric pressure; the pressure differential is slightly negative, somewhere between 0 and negative 0.2 psi. The printhead never receives positive ink pressure. That means the printhead needs to suck ink from the damper’s low pressure side. How does it do it? Capillary action is the only mechanism I can see doing the job. Specifically capillary action in the very fine piezo channels.
- 3. Air trap. This is where I think there might be a design problem. The low pressure chamber of the damper is designed to trap air. When/if a mixture of ink and air enters the chamber, air rises to the top and ink sinks to the bottom. Ink is sucked by the printhead through an opening at the bottom of the low pressure chamber. Therefore only air free ink should be able to reach the printhead.
Except that, in my view, there is a problem. Once there is a mixture of air and ink in the chamber, the air is trapped there forever! It has nowhere to go. The fraction of air to ink in the low pressure chamber can only increase over time during normal operation. When the printer is new, the ink lines, damper, and printhead are filled only with air. Priming the system, I assume, is achieved by creating a vacuum at the capping station. If the vacuum is strong, it will remove the air from the low pressure chamber before ink reaches it. When the ink reaches the vacuum of the low pressure chamber, it will completely fill that void. A new printer primed for the first time with a prefect vacuum will have an air free damper. If the vacuum was not perfect, ink will not completely fill the chamber and whatever air was left will be trapped in the chamber essentially forever. If the priming was perfect and the chamber was initially air free, but air subsequently finds itself in the ink lines, it will accumulate in the damper.
Let’s assume that a power cleaning creates a perfect vacuum at the capping station, will it get rid of the trapped air? I don’t think it can. If the vacuum cannot propagate to the chamber, it cannot remove the air. I don’t think it can propagate there because there will always be at least some ink between the vacuum at the capping station and the trapped air. The depression caused by the vacuum will simply suck more ink in the chamber, which will sink below the trapped air in the low pressure chamber (even if the ink lines are depressurized first, ink will still flow in the chamber).
The only way to remove the trapped air is to pivot the damper 180 degree to that the opening at the bottom of the low pressure chamber is now on top. This implies disassembling the head and sucking the air out with a syringe. Another way is to completely drain all the ink from the ink lines and dampers and thereafter performing an ink charge (praying that the capping station will create a strong enough vacuum). That would be a very costly procedure, several hundred bucks’ worth of ink down the drain.
Is air in the damper bad? I think so:
• Air expands and contract much more than ink with variation in temperature and pressure. Let’s say trapped air in the damper warms up during operation. If the amount of air trapped is small, there might not be any associated problems with its expansion during operation as the opening at the bottom of the LP chamber is always covered with ink. If there is a large quantity of trapped air, expansion and shaking might lead to air being sucked by the printhead and loss of nozzles during printing. In both cases, after shutting down the printer, as the trapped air cools it will increase the depression in the LP chamber. The more air, the more so. This might overcome the capillary action forces in the printhead piezo channels and draw air from nozzles.
• An increase in atmospheric pressure after shutting down the printer will shrink the volume of trapped air, potentially drawing air in the nozzles.
• It could be that the x900 are more sensitive to this problem than other Epson printers with the same damper design because of the smaller volume of the piezo channels which would empty more quickly.
• I have to say I don’t fully understand the dynamic of air and ink inside the printhead. But it could be that once the ‘entrance’ of a piezo channel is exposed to air (the exit being the nozzle hole), the capillary action for that channel ceases. Since the pressure inside the printhead is less than the atmospheric pressure outside, air may be drawn inside the head trough an ink-free channels, causing nearby channels to ink starve as the air bubble grows; you would therefore tend to see groups of adjacent nozzles go missing. The only way to recover is to vacuum the air out with a cleaning cycle which would re-prime the piezo channels. There is a chance that the shaking and bouncing of ‘printing through’ missing nozzles might slash some ink on the entrance of a missing channel, but it’s more likely to just draw more air in the head.
Sorry for the long post. I'm sure I've missed a bunch of things but is the damper design problematic or not?
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Interesting.
Wonder if one would be able to put a larger syringe, or some sort of vacuum tank with a quick valve, in the capping station's output hoses and do a quick suck on the thing with the head parked there to remove any air in the head? The pump there may not be enough to do much of anything other than a weak capillary drain. I also wonder if that pump alone is enough to do a service fill and purge too, maybe the air pressure is more there during that initial set-up step?
I agree that one way may be to put the head in a higher position so it can bleed out naturally, but how? I could see a bit of air being pulled in back through the head once a ink cart is pulled too and any slight pressure is relieved. I've switched out carts and had no ink for a while which makes me think air is there, but it somehow begins printing again. Dunno.
I don't know what goes on with the silly MK><PK switch. I got a really bad "No ink at all" in the blacks during a nozzle check doing that once. Took a couple of days before it worked again. Air? That whole PK-MK idea needs to be scrapped and just find a better "universal black" ink. Good to sell a lot of ink though. Jon Cone recently wrote "that about 35% of the ink ends up in the maintenance cart anyway." Seems a lot going down the drain.
SG
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Here is a schematic of an ink damper.
(http://lucbusquin.com/sites/default/files/damper_schematic.png)
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Wonder if one would be able to put a larger syringe, or some sort of vacuum tank with a quick valve, in the capping station's output hoses and do a quick suck on the thing with the head parked there to remove any air in the head? The pump there may not be enough to do much of anything other than a weak capillary drain. I also wonder if that pump alone is enough to do a service fill and purge too, maybe the air pressure is more there during that initial set-up step?
One problem is that even if the pump created an instantaneous and perfect vacuum, there is a strong possibility that it would still not remove trapped air in the damper.
Another problem is that an abrupt drop of pressure at the head might damage the extremely fragile piezo capillary channels. I think a slow ramp up is needed to give air a chance to escape peacefully. The printer's vacuum pump should be sufficient.
As a thought experiment to help think about trapped air, imagine the following setup: a reservoir filled with ink (similar to a cartridge), connected to a chamber containing trapped air (like an ink damper), and connected to a vacuum (such as the vacuum at the capping station). Between the reservoir and the chamber there is a variable flow restrictor or a valve (absent in the actual printer). Between the chamber and the vacuum there is a fixed flow restrictor (like our capillary piezo channels).
Now, what happens as we close the variable flow restrictor?
With the variable flow restrictor fully open the trapped air is barely affected.
(http://lucbusquin.com/sites/default/files/open.png)
With the variable flow restrictor in an intermediate position the trapped air expends but not enough to actually escape the system.
(http://lucbusquin.com/sites/default/files/mid.png)
With the variable flow restrictor closed the trapped air can finally escape.
(http://lucbusquin.com/sites/default/files/closed.png)
I haven’t discovered anything yet in Epson design that would significantly restrict the flow of ink from the cartridges to the dampers during a ‘vacuum cleaning’. There is definitely no shutoff valve.
I agree that one way may be to put the head in a higher position so it can bleed out naturally, but how? I could see a bit of air being pulled in back through the head once a ink cart is pulled too and any slight pressure is relieved. I've switched out carts and had no ink for a while which makes me think air is there, but it somehow begins printing again. Dunno.
Power cleaning with the printer upside down ;D
I don't know what goes on with the silly MK><PK switch. I got a really bad "No ink at all" in the blacks during a nozzle check doing that once. Took a couple of days before it worked again. Air? That whole PK-MK idea needs to be scrapped and just find a better "universal black" ink. Good to sell a lot of ink though. Jon Cone recently wrote "that about 35% of the ink ends up in the maintenance cart anyway." Seems a lot going down the drain.
It could be air. There is a couple more potential air traps in the K switch.
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Here is a short clip showing what the bottom of centrifuged green ink looks like magnified 600x: https://youtu.be/wDTTMrqU3Co (https://youtu.be/wDTTMrqU3Co)
Note the Brownian motion of pigment particles when they are not clumped together and the absence of motion when they stick together.
(The video was shot with a smartphone through the ocular of the microscope, DSLR adapter is on the way ;D )
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Interesting stuff you are doing here Cybis! Thinking of designing a new printer too? ;-)
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Interesting stuff you are doing here Cybis! Thinking of designing a new printer too? ;-)
:) John, those missing nozzles are really ticking me off and I just like to know my ennemies...
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I was pretty excited this morning to see the result of an experiment I ran overnight.
I replaced a printhead channel with a single glass capillary tube, filled refillable cartridges with colored distilled water, pressurized the cartridges at 5 psi. I then drew the colored water through the capillary tube and depressurized the cartridge thereafter.
An actual printhead contains 360 ‘capillary tubes’ about 50 x 50 microns, creating a suction force of about 0.5 PSI. The dampers open at approximately 0.05 PSI, so the capillary force is plenty enough to suck ink from the slight vacuum created by the dampers. Note that a single printhead nozzle also ‘sucks’ with a pressure of about 0.5 PSI.
The smallest glass capillary tube I could put my hands on was 100 micron in diameter by 100 mm in length. The suction created by the glass tube is about half of a printhead nozzle: 0.25 PSI.
I also experimented with a 400 micron plastic tube that exhibited essentially zero capillary forces.
When I drew water through the plastic tubing alone, the water would recoil back towards the damper as soon as suction was removed. This demonstrates neatly that there is indeed a slight vacuum in the damper and printhead.
When I drew water through the 100 micron capillary tube, the water would fill the glass tube on its own even without any suction being applied. Suction was needed to draw ink to the entrance of the tube, but once the liquid made contact with the tube, capillary force alone was sufficient to draw the liquid from the damper and into the remainder of the tube. Even with the cartridges depressurized the water would remain in the glass tube, at least for the first few hours…
When I checked the glass tube this morning, about 15 hours after filling it, it was empty. The water was sucked back in the damper! Why? :o
The low pressure chamber of the damper happened to contain about 50% of trapped air. Overnight, the temperature in the room dropped by about 4 degrees Celsius and the atmospheric pressure increased by about 5 hPa. Could it be why?
It could be a fluke - I need to repeat the experiment with and without trapped air a few times. But if the glass capillary tube is a good proxy for how the printhead behaves, and if further test runs confirm the first result, I think this is a good candidate for the main mechanism causing Epson x900 nozzles to go missing.
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Picture of the experiment.