Ink tanks are small, plastic boxes filled with a liquid ink. Each color may have its own individual ink tank or one ink tank can contain multiple colors but the printheads will always be separate. The ink tank feeds its liquid ink down to the separate printhead inside the printer which in turn dispenses the ink in the form of droplets onto the page to form text or images. Sometimes, the ink tank sits directly on top of and directly feeds into the printhead, such as with Epson and Canon Printers. Other times, one printhead may be shared by multiple colors or the cartridge may sit offset from the printhead and the ink feeds to the printhead via tubes or channels, such as with some HP and Kodak printers.
The Technology Behind It
The Ink Tank
The ink tank acts as a reservoir of ink for the printhead. A good analogy would be the ink tank would be the gas tank that stores and feeds gas (ink) to the engine (the printhead).
How does it work?
The ink tank will have a nozzle at the bottom or side from which the printer will pull ink from. Sometimes this nozzle can be punctured by a syringe-like piece in the printer to vacuum the ink from the ink tank, other times the nozzle on the ink tank is a fabric pad that the printer makes an air tight seal against to vacuum the ink out.
The Separate Printhead
The printhead is the engine of an inkjet printer that puts ink to paper. A printhead is the element which puts the ink to the page to form the text or image being printed. The printheads are separate from the ink tanks and can either be replaceable or built into the printer itself.
How does it work?
There’s two common types of separate printheads are thermal printheads and piezoelectric printheads.
Thermal technology uses silicon wafer heating elements to rapidly superheat and vaporize a small volume of ink. The vaporized ink expands, which in turn forces tiny droplets through the nozzle on the printhead. This is common with HP, Lexmark, and Canon printers.
Piezo technology applies an electric charge to a piezo electric crystal. The electric charge causes the piezo electric crystal to flex, forcing an ink droplet out the nozzle of the printhead. The piezo electric process allows more control over the shape and size of the ink droplets. Also, the ink doesn’t have to be heated, which allows greater freedom in the formulation of the ink. These types of printheads are used with most Epson printers.
The Ink Droplets
The liquid ink is dispensed onto the page in the form of microscopic ink drops. These drops can vary in size and are finely laid together or combined on the page to form images or text.
How do drops form images and text?
By differentiating the size of the ink drops, combining colors, and the placement of the drops onto the paper these drops will form the image.
The ink being used is liquid and can be pigment-based or dye-based ink.
What’s the difference?
Pigment-based inks are not water-soluble, although if you break open a pigment-based ink cartridge you’ll see a liquid. These inks are basically small pigment spheres suspended in water. They’re created by grounding chemically-based polymer resins into a small powder and then added to water. Because they’re not water soluble, these inks aren’t likely to smear when they come into contact with water—so they do a better job than dye-based inks of resisting both water and UV light. The color however, is not vibrant as dye based ink so normally pigment is used more often in black cartridges. With black ink, color brightness isn’t as much of an issue—and the fact that pigment-based inks are more resistant to water and light than dye-based inks make them more desirable in that regard.
Dye-based inks are water soluble, and they’re made by dissolving a colorant enhanced by optical brighteners into water. The resulting colors are much brighter and more accurate than what you’ll get with pigment-based inks. However, dye-based inks do tend to fade much more quickly in the sun and have a shorter shelf life overall than pigment-based inks do. Since dye-based ink is water soluble, it’s also more likely to smear if it comes into contact with water—even if it’s already dried on the page.
Pros and Cons of an Ink Tank and Separate Printhead Setup
Ink tanks are generally cheaper than cartridges with integrated printheads as you are only replacing the ink itself rather than the ink and printhead unit as one. Colors can also be made into individual tanks so that when a color is depleted, only that color ink tank will need replacing. However, with the printhead separate the printhead will need to be maintained. Sometimes, certain printers have the printhead permanently built in so the printhead is not replaceable if there is a problem.