Tuesday, November 4, 2014

2D Digital Printing Technologies

Illustrators use digital printing technology to reproduce their work for a number of purposes. Most of us own and rely on one or more digital printing output devices to help us conduct our business and produce our work. Illustrators who exclusively work digitally are totally reliant on digital printers to help proof work in preparation for offset printing or display it in non-digital settings.

Over the past few decades several different types of printers has been used to reproduce digital work. Some of these device types have become all but obsolete due to technological advancements in digital printers, which have become quite sophisticated in quality and economically efficient.

Impact Printers

The earliest digital were based on impact technology. These printers contain an appliance that comes into physical contact with the paper surface in order to transfer toner to create an image. The two main types of impact printers are character printers and dot matrix printers.

Character Printers

Character printers are basically computerized typewriters that print nothing but fixed characters. They have a ball or series of bars with actual raised letters and numbers on the surface. To print a letter is struck against an ink ribbon, transferring the character's image to the paper. The characters are finite and cannot be altered.

Inpact character printhead.
Impact character print sample.

Dot Matrix Printers

Also referred to as a pin printer, and precursor to inkjet and laser printers, dot matrix printers use print heads to strike an ink ribbon to place hundreds to thousands of little dots directly on the paper to form text or images. The matrix field allowed computer manipulated imagery and type to be combined and customized. Dot matrix printers, because of their low quality prints, have been replaced by inkjet and laser printers.

Dot matrix printhead.
Dot matrix print sample.

Non-Impact Printers

As the name suggests, non-impact printers do not touch the paper when creating an image. Both wet and dry toner technology printers are represented in this category, which includes inkjet, laser, thermal wax, dye sublimation, solid ink, bubble jet, piezoelectric, and thermal autochrome printers.

Inkjet Printers

Inkjet printers produce prints by spraying liquid ink onto paper. Inkjet printers can produce resolutions as fine as 600 dpi or more rather inexpensively. The print head has several tiny nozzles, called jets that spray ink drops onto the paper as it moves past it to produce characters and images. Because the ink is liquid, prints require time to dry for the ink to cure properly. Most inkjet printers contain cyan, magenta, yellow, and black inks, consistent with CMYK 4-color process printing. The more sophisticated units use as many as eight color cartridges with red, green, blue, matt black, and gloss optimizer along with the CMYK inks. These high-level inkjet printers can render gallery quality digital images on special paper stocks,

Inkjet 4-color printhead.
Inkjet dot pattern nagnified.

Bubble Jet Printers

Thermal Bubble Jet
A thermal bubble jet printer differs from a conventional inkjet printer in the way the droplets of ink are formed and distributed on the paper. In a standard bubble jet printer, tiny resistors produce heat, which vaporizes the ink into bubbles. The expansion of the liquid from the heat causes a bubble that pops or collapses causing a vacuum to be created, which forces ink into the print head from the cartridge to be ejected onto the paper surface. Bubble jet print head have 300 ink nozzles. High-end units have 600 nozzles, all which can dispense ink simultaneously.

Bubble jet printhead dispensing ink.
Bubble jet print dot pattern magnified.

Piezoelectric Bubble Jet
Patented by Epson, piezoelectric technology uses piezo crystal dyes. These dyes are located at the back of the ink reservoir of each nozzle. The crystal receives an electric charge that causes them to vibrate. When they vibrate in the nozzle they act like a piston in an engine, alternatively pulling ink into the nozzle from the reservoir and then dispensing it to a receiving surface. Piezoelectric printing is most commonly used for digital printing on fabrics.

Piezoelectric printhead.
Piezoelectric dot pattern magnified.

Laser Printers

Laser printers, also called laserjet printers, were developed as devices that adapted photocopier technology for computer generated digital output. Using static electricity and heat, laser printers differ from inkjet printers in that the toner or ink in a laser printer is dry, whereas in an inkjet printer the ink is wet. More commonly used for high volume output, most laser printers are monochrome, although there are also color laser printers that contain 4-color CMYK insets for the production of full-color prints. To print, a laser printer places an electrical charge on a selenium drum. The charged areas attract ink, which is then transferred to the paper surface. Most laser printers print at a resolution of 600 dpi., however high-end models can produce resolutions as fine as 2400 dpi

Laserjet printhead.
Laserjet dot pattern magnified.

Solid Ink Printers

The toner used for solid ink printers is in the form of sticks of wax-like ink similar to hard crayons. This heat based process melts the ink as it is applied to the paper. As the ink cools it then hardens in place. Unfortunately prints produced using solid ink are susceptible to damage by heat such as would occur in lamination. Solid ink printing can be applied to many different types of media and substrates.  

Solid ink printhead and ink bar.
Solid ink dot pattern magnified. The American Institute for Conservation.

Dye Sublimation Printers

The toner colors in dye sublimation printers is supplied by rolls of red, blue, yellow and gray colored cellophane film panels that are alternatively sectioned together end to end. The 4-color CMYK version contains cellophane film coated with solid cyan, magenta, yellow and black dyes corresponding to four basic color printing. The film is heated at various temperatures, according to the amount needed to reproduce a particular image. The heated dyes melt and permeate the surface of the paper, then they solidify to form a print. Dye sublimation printers apply each color individually as its own layer until the image is completed. The dyes actually permeate and stain the paper to generate an image.

Dye sublimation printhead with color ink ribbon.
Dye sublimation ink pattern magnified. The American Institute for Conservation.

Thermal Wax Transfer Printers

A hybrid of dye sublimation and solid ink technologies, thermal wax printers use a solid form of ink applied to a ribbon with alternating 4 color CMYK process color bands. Tiny heated pins contact the toner ribbon as it passes to produce an impression on the paper surface. The heat causes the wax to melt and adhere to the paper, where it hardens in place.

Thermal wax transfer print head.
Thermal wax transfer ink pattern magnified. The American Institute for

Thermal Autochrome Printers

Thermal autochrome printers operate in a parallel way to photographic printers. The color is contained within the autochrome paper and acts as a receptor for a heat source, instead of a light source, that brings forth the color. The paper contains three color layers--cyan, magenta and yellow. Color density within the print is controlled by a varying amount of heat that is applied. in the paper, and each layer is activated by the application of a specific amount of heat. The print head applies each color individually by passing over the paper for each separate color until the image is complete.

Thermal autochrome print head.

Thermal autochrome dot pattern magnified. Image Permanence Institute.