Laser printing and inkjet techology filter
May 7, 2009 5:35 AM   Subscribe

How do laser and inkjet printers work? I know the basics, of course, but I am looking for serious expertise at the level of the actual chemistry and physics... things like fuzer specs, toner chemistry, deposition, transfer, particle masses, exotic materials; in short... the stuff an actual expert would know.

I have a friend who is a hot shot civil engineer who is doing some proposal work and who, for some reason, needs to locate some expertise in the area of inkjets and laser printer technology. (I've been beating him up for years to join Metafilter, and with a good answer here, might just push him over the edge. And Jessamyn NEEDS that $5!)

He's trying to get smart on the laser fuser and the details of toner chemistry, but transfer mechanism is important, too. Rasterization less so. For inkjet, the ink chemistry and fluid dynamics of transfer.

I know there are 20 mefites with PhDs in laser printing out there, fingers poised above keys awaiting this very question. All leads and info very much appreciated.
posted by FauxScot to Technology (5 answers total) 3 users marked this as a favorite
Best answer: I once had an internship writing firmware for big-ass inkjet printers (wow, looks like HP bought them)!

Inkjet printing is pretty straightforward. You have a tiny tube of ink and you boil the ink that's almost at the end, which propels the drop at the end. I used to work for someone that made these - ink quality is all about consistency and having the right viscosity (so the drop holds together and you can shoot a bigger drop). It's worth mentioning that most inkjet printer ink is full of toxic chemicals to achieve these properties, and should always be disposed of properly. Anywhere I've ever been that sells ink cartridges also accepts old cartridges for "recycling.

The other and arguably more important half of injket printing is the paper. If you use uncoated paper the ink soaks in and bleeds around a bit, which changes the color. So you want a coating that will not absorb ink, but also doesn't have hydrophobic properties. It's important that multiple drops deposited next to one another do not form up into a ball, but stay coating the paper. Try writing on high quality inkjet photo printing paper with a Sharpie. It's extremely satisfying.

For best results inkjet printers often will lay down a pattern of maybe 25% coverage each pass, which gives the deposited ink a little time to dry so that colors don't bleed together.

Typically the inkjet oriface is mabye 1200 microns from the surface of the paper. The further you get the less accurate you are (since the jets don't shoot exactly straight), but if you get too close you risk a head-strike (or as we called it: paper-cutter mode) if the paper has any small wrinkles in it. If you hold the inkjet nozzle as a gun, it will shoot about 6" (at which point it's got a pretty big spread - probably wider bigger than a can of spray-paint!)

You also can't move the print head too quickly because (60 IPS is around the upper limit) because then the droplets lateral motion relative to the air complicates things, breaks up some droplets, and makes their placement less predictable. Drum printers improve that a little bit, but taping your media to the drum is a hassle nobody likes, and still if you spin it too fast the ink will spatter when it hits the paper.
posted by aubilenon at 11:10 AM on May 7, 2009

At least for laser printers I suggest you start with a service manual. The service manuals for HP laserjet printers are amazingly detailed and contain way more information than I will ever need in order to fix one. Oddly enough they are also missing a fair amount of basic practical troubleshooting information.

I have an HP 4200 service manual here on my desk. It is full of circuit block diagrams, info about the charges needed to get the paper to stick to some rollers and not others, temperature thresholds, ac/dc bias charges, etc.

Not quite PhD level but might still be a good place to start. It is possible to download service manuals though I'm not gonna post any links here. You can also call an authorized service provider and they will probably sell you a manual.
posted by J-Garr at 12:32 PM on May 7, 2009

Response by poster: Thanks, folks. My compadre found a little online info, but both of these are useful suggestions.
posted by FauxScot at 1:17 PM on May 7, 2009

Oh! Laser printer repair manuals are great. I don't know why but I adore repetitive defect rulers.
posted by aubilenon at 2:11 PM on May 7, 2009

Just to add to what aubilenon said: The process of droplet formation in most consumer inkjet printers is by boiling the ink with a resistive heater causing the ink to shoot out a nozzle. Higher end inkjet printers, and some consumer models like the ones from EPSON, use a different method utilizing a piezoelectric membrane that deforms with an applied voltage pushing the ink out of the nozzle.
The piezoelectric inkjet heads allow for better control of droplet formation and allow for the use of inks that are temperature sensitive.

There is a book on the subject of inkjet droplet formation but I can't seem to find the name currently. I did find this book though on the chemistry of inkjet inks.
posted by toftflin at 1:33 AM on May 8, 2009

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