CIS Systems and pigment ink

Over the years at OctoInkjet we’ve frequently been asked about using pigment inks in Continuous Ink Supply (CIS) Systems so this article should deal with our experience of their use and explain why we don’t recommend them except in specific scenarios.

The Problem

Setting The Scene

Before we kick off it’s important to provide some background information. The first thing to note is that Pigment ink is made up of tiny particles of solid matter known as pigment that are suspended in a carrier or ink base solution. This is very different from Dye inks which are dissolved completely into the carrier solution.

Naturally pigment particles are subject to gravity so, while the pigment particles shouldn’t settle out, they will tend to concentrate towards the bottom of any vessel over time.

Right, the next thing to understand is that almost all CIS systems are designed such that the ink is drawn from the reservoir via a hole in the base of the reservoir.

Finally, unlike a fairly standard inkjet cartridge (eg: a T0891 Epson Durabrite) the volume of ink in a CIS system is usually around ten times greater than you would get in a cartridge, and while your normal cartridges get shaken about by the printhead as it prints, your reservoirs sit by the side of the printer and never move.

So What Happens

You have a pigment ink solution that tends to concentrate towards to the bottom of a container and is never shaken up. If you had only 10ml of ink (roughly a normal cartridge) the concentration wouldn’t be too high but reservoirs hold ten times the volume which means a higher volume of concentrated pigment and all of it focused near the bottom of your reservoir.

Your CIS system feeds the printer from the bottom of the reservoir so, higher pigment concentration builds up in the cartridges over the printhead and slowly but surely the printer is choked with a very rich solution that contains too much pigment and not enough of the carrier solution.

Net result: Clogs = more head cleaning = more waste = more expense = more frustration

It’s Not Immediate

None of this happens immediately. Concentrations take time to build up so the process is a very slow one that is rarely diagnosed correctly as it progresses.

When a Pigment CIS system is first installed, all the inks are freshly installed, well mixed and flow perfectly. Over time the concentration starts to build up and what starts as maybe a single head clean to clear a few missing nozzles (ie: banded output) slowly develops into needing to clean the heads once a week, then maybe running two head cleans until you feel like you do more printhead cleaning than printing.

Solutions

Use Something Else

The obvious way to avoid this sort of problem is to consider using refillable cartridges instead of CIS systems as they only hold a limited amount of pigment ink are regularly shaken up by the printhead movement (assuming you are using the printer regularly) and can easily be refilled with ink that has had a really good shake before being used.

We are of course assuming you shake your inks before you refill them ūüėČ

Still Want to Use a CIS?

Ok, it is still possible to use a CIS system but you need to invest more time in your system to reduce its potential, and even then some basic maintenance can be needed to get things freshened up and running properly again.

Prevention

The obvious prevention technique is to regularly agitate the inks in the reservoirs. This is particularly useful just before you do a print run or head clean as the process of printing or head cleans, draw more ink into the CIS cartridge block and subsequently the printer. If it’s well mixed before hand you’re not adding to the concentration in the cartridge block.

Another technique is to print a LOT of output on a regular basis (used in tandem with regularly agitation). Regular use will keep the ink flowing and reduce the likelihood of the printhead nozzles clogging up.

Maintenance

One of the best ways to resolve persistance clogging and over-concentration of pigment ink in a CIS is to refresh the ink in the cartridge block by pulling a considerable amount of ink through the system.

To do this you need a syringe (preferably one for each ink colour) and a Pull-through-adapter then follow this process.

  1. Top up the CIS system reservoirs (as required)
  2. Plug vent holes on all reservoirs
  3. Remove the CIS cartridge block from the printer
  4. Thoroughly mix the inks in the reservoir by gently
  5. Attach the Pull-through-adapter to syringe
  6. Remove the vent plug for the target ink reservoir
  7. Hold the cartridge block upright (as if in printer)
  8. Insert the Pull-through-adapter into the ink outlet on the target cartridge
  9. Pull back on the syringe to pull ink through the outlet and flush through the system
    We recommend pulling through at least 20ml of ink
     
  10. Plug the vent hole for the target ink reservoir and open the fill hole
  11. Dump the removed ink back into the reservoir
    Check you are dumping to the correct reservoir first!
     
  12. Flush the syringe and pull-through-adapter
  13. Repeat steps 5 – 14 for each cartridge/ink
  14. Replace the cartridge block in the printer
  15. Remove the vent plugs from all the ink reservoirs
  16. Run a single printhead clean and allow the printer to sit for half an hour before running a nozzle check*
  17. Use printer as normal


*If the printer is still showing banding, avoid using multiple head cleans to clear the issue. Instead do a single head clean, print a nozzle check and try printing a full sheet of block colours to allow the printer to re-establish ink flow. Leaving the printer to rest for half an hour or even overnight can also allow things to settle and the printer nozzles to all return to normal function.

Summary

As you can see from the information provided above, the process for maintaining a pigment ink based CIS system can be quite involved and drawn out. Refillable cartridges can introduce their own issues if the cartridges are not primed properly (ie: air removed from the outlet) so there’s no magic bullet but a good understanding of what is involved will help you avoid a large number of issues that pigment inks and CIS systems can create.

Updated on 9 February 2022

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