[missymig]

Hello,

I'm working on a back yard project for refilling inkjet cartridges inside a vacuum. A very basic system to remove the air prior to refilling (in effect, priming the cartridge before filling, instead of trying to prime it after filling). I am wanting to apply approx -95 to -98 kPa vacuum.

There are many aftermarket inks in the refilling industry, and I have a concern about the application of Henry's Law and also Raoult's Law.

A colleague has suggested that the ink will progressively lose its ability to retain the gasses dissolved in it, and they will be expelled from the ink. They suggested that:

1. If I use too much vacuum I will give the ink the 'bends' and may even cause it to boil.
2. After the vacuum is released and the cartridge (and ink within) has been restored to atmospheric pressure) bubbles of gas will continue to grow for several days inside the ink, (thereby negating the intent to remove the air in the first place). IS THIS TRUE?

He also suggested that Raoult's Law will apply. Compounds dissolved in the ink, such as solvents and dyes, will release gas or sublimate when exposed to pressure reduction.  He said that as this is another form of the bends, this effect will also last for several days after venting (IS THIS TRUE?).  Add this to the Henry's Law issue and I will have a double disaster.

The vacuum chamber is approx 2 litres in size. Would evacuation or vent speed influence the effect of these laws? How would you suggest finding the optimum level of vacuum?

Your opinions / theories be appreciated.

Thanks so much.

[Borek]

1. If I use too much vacuum I will give the ink the 'bends' and may even cause it to boil.

It may boil, it depends on the initial temperature.

2. After the vacuum is released and the cartridge (and ink within) has been restored to atmospheric pressure) bubbles of gas will continue to grow for several days inside the ink, (thereby negating the intent to remove the air in the first place). IS THIS TRUE?

I don't think so, but it is not clear to me what will the pressure in the cartridge be after filling. Is the cartridge opened so that pressure equilibrate with the outside?

[missymig]

The cartridge is a typical Hewlett Packard cartridge that has a printhead (with minute nozzles), an internal foam (to retain the ink), and fill holes on the lid through which needles can be inserted into the foam.

During filling, the cartridge is sitting inside a vacuum chamber with the printhead sealed. Air is removed from the chamber (and consequently from the cartridge, via the large fill holes). Ink is then dispensed into the foam.

After filling, the vacuum chamber is vented slowly, returning the cartridge (inside and out) to normal pressure again. The venting also pushes the ink down through a filter screen and into the printhead and nozzles.

The needles are then removed from the cartridge and the inside of the cartridge should have a nice volume of high-density ink in the foam. The fill holes in the lid remain open. The cartridge is never sealed completely.

[Borek]

I doubt anything will happen after the pressure is back to normal. The only moment you should be concerned about is when the ink is under vacuum. After that - even if there are bubbles inside - they should slowly disappear. Well, if they are kept in the foam it may not happen, but in general bubbles that are present below the surface are not stable - depending on what they contain they dissolve in the liquid, or they condensate - or, if allowed, they go up and burst at the surface. I can't think of a single reason why they should grow after pressure is back.