Putting the Ink into Inkjet

ARGUABLY ONE OF THE MOST CRITICAL COMPONENTS OF INKJET PRINTING IS THE INK USED. INK CHEMISTRY AND FORMULATIONS CAN NOT ONLY DICTATE (IN PART AT LEAST) THE FINAL QUALITY OF THE PRINTED IMAGE - E.G. THE BRILLIANCE OF COLOUR, THE IMAGE’S LIGHTFASTNESS, ETC - BUT AN INK’S VISCOSITY AND OTHER PROPERTIES CAN ALSO HAVE AN IMPACT ON THE DROP EJECTION CHARACTERISTICS AND THEREFORE THE RELIABILITY OF THE PRINTING SYSTEM USED.

For this reason, many different types of inks have been developed and experimented with, for use in inkjet applications. These include:

Aequeous/Water-based Inks

Aqueous- or water-based inks are most commonly used in Small Office and Home Office (SOHO) desktop inkjet printers (e.g. the Hewlett-Packard DeskJet, Canon BJC and Epson Color Stylus). In the case of thermal inkjet, due to the basic vapour bubble formation process, water is an obvious material of choice. Viscosity of water- based inkjet inks range from 2 to 8 cps.

Important Ink Properties

Print quality

• Brilliant colours

• High colour density

 

• Colour stability

 

Light fastness

 

 

Water fastness

 

 

Slow aging

 

 

Runnability

• Surface tension

• Ink formulation flexibility

When a water-based ink droplet lands on the surface of an uncoated media such as bond, copy, or plain paper, the ink tends to spread along the paper fibres and penetrate into the bulk of the paper. Such ink behaviour lowers colour density and spot resolution on paper. Whilst some evaporation takes place, a water- based ink depends on penetration and absorption for its drying mechanism.

Paper or other media with a coated water-receiving layer can greatly improve both colour density and resolution by controlling the ink spreading and penetration at the coated layer.

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