PRINT QUALITY AND PERFORMANCE

Printhead technology has an impact on print quality and print speed. Print quality is generally measured in dots per inch (dpi) but the relative size of the ink dots and the number of printhead passes required to print an image will affect both print quality and throughput speed.

Large format digital inkjet printers use either piezo electric printheads or thermal printheads to express tiny droplets of ink directly onto print media. The first piezo printheads (binary printheads) could only express droplets of a fixed size and, using a four colour (CMYK) print process, the resulting print output could appear grainy, with poor tonal gradation and muted highlights.

To improve image quality, inkjet manufacturers introduced a six colour process (super CMYK). The addition of light cyan and light magenta inks to the binary print process allowed lighter colours to be substituted in highlights and mid tones. The six colour process used more ink but delivered print output with smoother tonal gradation and more vibrant highlights.

"What stood out for us on the Ricoh Pro L5160e was its high speed, ink coverage and cost per square metre, as well as the fact the print it produces is extremely high quality. It can produce all the large-format applications we offer to customers."

Lee Coulson, Managing Director, Inprint Colour

Considerations:

Can the printer produce greyscale images of near photographic quality?
Do I need to use light cyan and light magenta ink or just standard colours?
What is the throughput speed when printing greyscale images?
Can it print in different resolutions for different applications?

Tip:

Consider how the print be viewed. For work viewed at close quarters, such as fine art, it is important to select a device that produces high resolution output but for display graphics that will be viewed from a distance, resolution is less important.

Variable drop binary printheads

Variable drop binary printheads are a relatively new innovation. They enhance print quality by expressing ink droplets of different sizes, however the binary technology only allows one size of droplet to be printed in each pass of the printhead.

Whilst inkjet printers with variable drop binary printheads can produce vibrant, high resolution output without the need for additional colours (light cyan and light magenta), multiple passes of the printhead are required to produce grayscale images, significantly reducing productivity.

Advantages

High ‘native’ resolution
Print variable drop sizes
No need for light cyan and light magenta ink

Disadvantages

Can only print one drop size per pass
Multiple passes required to simulate greyscale printing, reducing productivity

Variable drop greyscale printheads

Variable drop greyscale printheads can express ink droplets of variable size in the same pass. This enables high resolution graphics and dense solids to be printed in a single pass, significantly improving productivity. The process also uses considerably less ink, reducing production costs.

Whilst variable drop binary printheads can deliver print output with a seemingly higher ‘native’ resolution, variable drop greyscale printheads can achieve the same ‘effective’ resolution using lower resolution printheads and in fewer head passes.

Indeed, according to FESPA (the Federation of European Screen Printers Associations), a 360 dpi print from a variable drop greyscale printhead has the same ‘effective’ resolution (real world appearance) as a 1,000 dpi print produced using a variable drop binary printhead.

FESPA: The ultimate guide for printhead technologies

Advantages

High ‘effective’ resolution
Print variable drop sizes in one pass
More productive for greyscale printing
No need for light cyan and light magenta ink
Uses less ink than binary or variable drop binary printheads

Disadvantages

Higher initial cost of acquisition

Tip:

Manufacturers quote a range of different print speeds. Compare speeds on a like-for-like basis at a level of quality which meets the majority of your customers’ expectations.