Inkjet printing

Inkjet printing is a digital technology used to recreate images. It works by propelling tiny droplets of ink onto various substrates. These substrates can include paper, plastic, wood, or even metal.

While inkjet printers were the most common type of printer in 2008, their market share has changed. By 2019, laser printers outsold them by nearly a 2:1 ratio. Specifically, laser printers made up 9.6% of all computer peripherals, while inkjet printers made up 5.1%.

There are two primary technologies used in contemporary inkjet printing. The first is continuous inkjet, also known as CIJ. In CIJ, a high-pressure pump directs liquid ink through a microscopic nozzle. This nozzle usually has a diameter of about 0.003 inches. The stream of ink breaks into droplets due to a process called Plateau-Rayleigh instability. A piezoelectric crystal may vibrate within the gunbody to create an acoustic wave. This wave causes the liquid to break into regular intervals of droplets.

In the CIJ process, droplets are managed by electrical or magnetic fields. As the droplets form, they are subjected to an electrostatic field. This field varies depending on how much deflection is needed for the print. Charged droplets can be separated by uncharged "guard droplets" to prevent them from pushing each other away. The droplets then pass through another field to be directed toward the substrate. Many droplets are not used for printing and are instead sent to a collection gutter for reuse. This method is very fast, with droplet velocities reaching approximately 20 meters per second.

The second major technology is drop-on-demand, or DOD. Unlike the continuous stream of CIJ, DOD expels fluid from the nozzle one drop at a time. This can be achieved through mechanical means or electrical methods. DOD is a very popular method for consumer and industrial use. It can use a single nozzle or thousands of nozzles working together.

Software can even direct the printheads to apply between zero and eight droplets per dot. This ensures ink is only applied exactly where it is needed.

Thermal DOD is a common type of drop-on-demand printing. Many consumer printers from brands like Canon, HP, and Lexmark use this thermal process. In a thermal printhead, tiny chambers contain heating elements created by photolithography. To eject a drop, a pulse of current passes through the heater. This causes the ink to vaporize rapidly, forming a bubble. This bubble creates a large pressure increase that propels the droplet out.

This is why Canon uses the trade name "Bubble Jet." These printers often use water-based inks containing pigments or dyes.

Another version of DOD is piezoelectric printing. This method uses a piezoelectric crystal, which is an electrically polarized ceramic device. When a voltage is applied, the crystal changes shape. This shape change generates a pressure pulse in the ink chamber. This pulse pushes the droplet out of the nozzle.

Companies like Epson and Brother use this method. Piezoelectric printing is versatile because it does not require the ink to have a volatile component. It can also handle a wider variety of materials, such as solder paste or even living cells for tissue engineering.

The history of inkjet technology spans many decades of discovery. The concept originated in the 20th century, with extensive development in the early 1950s. Ichiro Endo at Canon suggested the "bubble jet" idea. Around the same time, Jon Vaught at HP was developing a similar concept. In 1982, Robert Howard developed a system using piezos to eject ink. He formed the company Howtek, Inc., which led to the Pixelmaster color printer.

This printer used "Thermojet" technology and solid ink. Earlier, in 1972, Steven Zoltan invented a tubular single nozzle acoustical wave drop generator. These various innovations eventually allowed printers to reproduce complex digital images by the late 1970s.

Today, inkjet technology is used in many different fields. Beyond printing photos, it is used in the emerging material deposition market. This includes printing electronic components or creating biosensors. High-quality fine art reproductions are often sold under trade names like giclée or Digigraph. These names help distinguish high-quality inkjet prints from everyday office printing. The technology continues to expand from simple paper printing to complex scientific applications.