How an inkjet nozzle fires 36,000 times a second
23rd Nov 2009 | 16:55
Inside HP's secret ink manufacturing facility
How cartridges are made
The precision needed for an inkjet nozzle to work is like dropping a grape from a 30-storey building and hitting a bucket on the pavement below. Now that's accurate. But in the case of an inkjet nozzle it's also doing it 36,000 times a second, not bad for something which is the third of a width of a human hair.
The drops fall at a speed of 50kmph – 35 million of them for every 6 x 4 photo you print.
We took the short hop over to Dublin, Ireland to check out HP's DIMO (Dublin Inkjet Manufacturing Operation) facility where it develops and manufactures ink cartridges.
Each new ink takes three to five years to develop and goes through thousands of different formulas.
"Ink is the hardest working part [of inkjet printing]," explains HP's Thom Brown. "One change or minor alteration could make a huge impact. It's wet but when you want it to be on the paper you want it to be dry," he explains.
HP came to Dublin in 1995, helped by IDA grants and has established a massive, 200-acre site. Intel's operation had already been in the area for a few years. The site is a mix of R&D and some low-level manufacturing.
How cartridges are made
At the facility we saw tri-chamber cartridges being made with integrated print heads. The early part of the manufacturing process involves putting a filter then sponge into the cartridge. It's essential that the right material is used to deliver the correct amount of ink to the nozzles – too much or not enough ink can result in the nozzles being starved or clogged.
Everything about the process is designed so no contaminants can get into the cartridge or that the different chambers inside the cartridge can't contaminate one another. The cartridges itself flies around the facility on small conveyors.
According to our guide, they can always track back if something has gone awry in the process – the cartridges all have an individual 16-digit ID laser etched on them along with a date. The lid is placed on and sealed before the cartridges are filled and everything is tested to stop leakage.
Attaching the print head is also a delicate process. Adhesive is applied on the area where the head will go, while the Tab Head Assembly (the flexible print head) is attached precisely. Any problem here and the head won't line up inside the printer. The THA is made with specifications at single-digit micron levels using a microscopic welding process.
The chip wafers are manufactured elsewhere. The so-called banner material is drilled using sand or laser in a process that creates the minute channels for ink to flow through. The material is laid across the wafer, but as it is UV curable, it needs to be kept away from UV, hence the lab we saw was bathed in yellow light. Another layer, the plating, has the holes through which the ink is actually forced and the different layers are then bonded and connected to each other.
Filling and testing
Filling and testing
Then we move on to the filling process. This is the "Wet Loop." What about the toxicity of inks, we ask – is it possible to have non-toxic inks? "We use the lowest amount of toxicity versus effectiveness" says our guide.
Four cartridges are filled at any one time, taking four to five seconds to fill each of them in a vacuum.
A high pressure is used to fill the cartridges from 1,000 litre tanks which are rolled around the facility. A huge ink splodge on the ceiling is the result of a time when the pressure got a little too much.
After the cartridges are filled, the nozzles are fired to test them. A vent in the top of the cartridge enables air to replace the ink as it's used, though access is via a labyrinth channel to prevent ink evaporation.
After a test print, the nozzles are sealed by the tape that you remove when you install them in your printer.
Finally, the cartridges are sealed and loaded into boxes and sent elsewhere to be placed in their sale packaging.
The electrical process is tested out at several stages throughout the process and techniques such as X-rays are used to see inside the cartridge as it prints in a special test area filled with tens of printers and old machines. An autopsy area seeks out the causes of problem cartridges. Long-life testing also takes place here.
"The physics of what happens inside a printer is quite extraordinary," says HP's Pat Harnett. "There's mathematics, temperature, process and fluid dynamics. It takes a lot of tuning to get it right on different papers."
"It's not as simple as millilitres of ink – there's a lot more behind that in terms of the nozzle balance. And it's not just about millilitres, it's about pages."
But how much of the cartridge uses recycled material? According to Harnett, it was 70 per cent in 2008. "You want an HP cartridge that's made of a recycled material but with all the benefit of buying an original HP cartridge. There's a mixture of both using content and complete recycling," he explains.
"Virgin material is much easier from a technologist's point a view. In recycled content there's the possibility of interaction with the ink. We need to get the wall thicknesses correct for example. A lot of research has to go into it. The difference between 70 per cent and 80 per cent [is] a lot of effort."
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