Designs on Inkjet Paper

IF WHAT INK IS USED FOR INKJET PRINTING IS IMPORTANT, SO IS THE CHOICE OF STOCK. THE IDEAL WISH-LIST WHEN LOOKING AT DESIRED PROPERTIES OF PAPER USED IN INKJET PRINTING, WOULD INCLUDE:

•Optimum print colour density (good fixation);

•Fast drying time without paper curl or cockle (fast absorption);

•High brightness;

•Lightfast and waterfast qualities;

•Wet rub and scuff resistance (no ink smearing);

•Lateral ink spread to enhance text resolution and colour-to-colour bleed by controlling the dot diameter. (The resolution specified by a printer can only be achieved through using the right substrate);

•Sufficient stiffness for feeding through printer.

Of these: printed colour density, ink drying time and colour bleed all depend heavily on the coating structure of the paper. 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.

For this reason, within the past few years, the market for specialty-coated inkjet media has exploded, especially in the home photo quality and large-format inkjet printing areas.

Another important factor in achieving quality prints is resolution. This relates to how much pictorial information a file holds. The DPI (dots per inch), tells us the resolution of an image; the higher the dpi, the higher the resolution and hence the finer the detail of the printed image. High resolution is generally considered to be 1200-5000 dpi.

In conventional printing, variable sized dots are set down in fixed patterns that in CMYK form 'rosettes'. These are formed because the screen is orientated differently for each colour. So screen angle, dpi and dot size all affect

the way that the transparent inks overlap and make colours and images in conventional printing. Screen angles are optimised for specific plates, presses, processes, etc., to prevent moiré and maximize sharpness and vibrance.

Unlike commercial four-colour process, most inkjet printing forms images by printing small dots of the same size at varying distances from each other – often overlapping so dot gain is more critical (This is known as stochastic screening). Dot gain relates to the tendency of the dots to print larger than they appear on the original. A drop in print contrast indicates that dot gain is too great – the dots merge and the image loses definition. On press dot gain is normally due to ink spreading as it hits the paper, and is affected by many factors; ink viscosity, substrate absorbency, paper coating and half tone screen ruling (fine and stochastic screen give higher dot gain)

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