Why do hp ink cartridges have an expiration date?

Just curious, as I was looking for one on ebay and they made mention of this a few times. What happens when it expires, does the ink lose its color effects or dry out?Why do hp ink cartridges have an expiration date?
It is about the ink drying up. If you try and use one that is much beyond the 'use by date' you run the risk of it not working properly. This is because with an HP ink cartridge, the 'working bits' are on the cartridge, not on the printer. If you look at the bottom back of the cartridge, you will see gold coloured connectors that link the cartridge to the printer and right at the bottom a little silver square. Look closer and you will see tiny pin head sized holes, or ink jets. This is where the ink comes out and, if a colour cartridge, gets mixed to produce the right colours.





One of the advantages of this system is that every time you buy a new cartridge, you effectively buy a new printer head. Downside is of course cost. And, if you buy a reconditioned cartridge, you are getting an older and used print head. I assume other makes of printers make their print heads far more robust because they have to last a long time, HP only have to make them fit for the life of one cartridge.





Handy tip: If you have an older cartridge and it doesn't want to print, or it seems to have run out of one colour or another, take it out and dip the print head end in a cup of extremely hot water for half an hour. Then, run it under a powerful hot tap for a few minutes. Let it air dry (drying with a towel risks clogging those little jets) and give it a try. If it doesn't work, repeat it a couple of times. For really stubborn problems, you might need to run the clean print head software in XP Printers.





The above works because all that is happening is that the ink on the surface has dried up and clogged those tiny holes. Using the water treatment fixes it and makes the 'use by date' less important.Why do hp ink cartridges have an expiration date?
Its fine - The expiration is there because over time the ink will dry inside the cartridge - They should be good even after the exp date
so that the ink dosent get dryed