Sponsored by Huntsman Textile Effects
Black ink matters in digital textile printing. Black is most often the key colour in the eight-colour CMYKOBRGr process, alongside cyan, magenta, yellow, orange, blue, red and grey. It not only adds depth and contrast, but is the basic component in every colour, colourway and design.
Many printers will choose a Neutral Black for the sake of flexibility. But, depending on the application, this may not deliver the best end result or avoid production issues that could impact productivity. Here are three reasons to look beyond Neutral Black:
1. To avoid the Wimbledon effect
The Wimbledon or football field effect refers to a slight colour difference between alternating sections of a shaded black design – akin to the stripes you see on a grass tennis court or football pitch that are achieved when the grass is mown and rolled in alternate directions.
In digital textile printing, one pass is printed from left to right, whereas the next is printed from right to left. Since the CMYKOBRGr print heads are positioned next to one another in the print head carriage, this directionality makes a difference. When printing a shaded black with black and red ink, for example, the black ink drops will reach the fabric a little earlier than the red ink drops in the left-to-right pass and a little later in the right-to-left pass. This is enough to cause a discernable difference in the final black colour.
Uni-directional printing is possible, as is increasing the number of passes, but both of these approaches will significantly slow down production and impact productivity. To avoid the Wimbledon effect without compromising printing speed and quality when a shaded black is required, it is preferable to choose the right shaded black ink for use as a stand-alone colour.
2. To avoid the "dithering effect"
Dithering is used by digital printers to vary colour density and create grey or mid-tone blacks. For example, a random arrangement of black ink drops with varying spacing will trick the eye into seeing grey tones.
The "dithering effect", on the other hand, is when individual printed dots are visible in the design, creating a grainy pixelated-looking image. It is more likely to occur when printers choose darker, more concentrated Neutral Black inks. To achieve a quality print of varying colour depth when printing shades of grey, the answer is to have a mid-tone black on hand or to invest in a separate grey ink.
3. To achieve consistency between batches
A shaded black ink allows mills to consistently and accurately achieve the right tones without depending on software shading. When compared to a standard Neutral Black ink, a shaded black therefore enhances consistency between batches during steaming without compromising speed or quality.
Another consideration is the ink chemistry. Vinylsulfon (VS) black inks are ideal when intense colours or neutral shades with light or dark tones are needed. However, these inks do require an optimised printing and steaming process to minimise the risk of reduction.
In contrast, monochlorotriazine (MCT) black inks offer a good balance of colour and fixation conditions, with excellent stability to reduction, especially during steaming. MCT inks also allow fabrics to be stored longer between printing and steaming without any risk of hydrolysis, enhancing reproducibility and process efficiency.
Mattia Perri, global technical manager, Inkjet Application of Huntsman Textile Effects says: “The traditional approach of relying on a Neutral Black regardless of the application is no longer suitable as textile printers today need to deliver a quality end result and avoid production issues that could impact their bottom line. There are options beyond Neutral Black. It all comes down to understanding what you need to achieve and what the different black inks can deliver.”
He continues: “The choice of black ink supplier is also crucial. When selecting between different brands, printers should consider colouristic performance, fastness performance and reproducibility, as well as print reliability and overall colouristic cost control.”
Ensuring that textile printers can select the exact shade for their application without compromising performance or production efficiency, Huntsman Textile Effects offers six different types of high-performance black inks in the NOVACRON® range. These allow for the production of the full range of black shades, including mid-tones and light shades without dithering, cool-bluish and warm-reddish tones, very dark tones and neutral black and darker basic colours on a range of cellulosic fibres, including viscose.
