WHAT ARE OBA'S AND WHY DO THEY CAUSE COLOUR PROBLEMS FOR DIGITAL TEXTILE PRINTERS
Optical Brightening Agents And Their Effect On Digital Textile Printing
WRITTEN FOR FESPA BY TEXTILE AMBASSADOR DEBBIE MCKEEGAN
What are Optical Brightening Agents, and why do they cause so many problems for Digital Textile printers?
A vital issue for the Digital Printing of Textiles is getting to grips with the technology and effect of the upstream use of Optical Brightening Agents in fabric bleaching and preparation.
OBA’s affect colour and how it is perceived, both by the naked eye in natural day light, and its acutely affected by the light source in which it is viewed.
During the process of Bleaching and Drying fabric whiteness can often be enhanced by the addition of an Optical Brightening Agent (OBA).
Optical brightening agents (OBAs) are chemicals that are added to textiles during bleaching of finishing and use the process of fluorescence to trick your eyes into believing your fabrics are whiter and brighter than they actually are.
These additives are often used to enhance the appearance of colour of fabric and paper, causing a "whitening" effect; they make intrinsically yellow/orange materials look less so, by compensating the deficit in blue and purple light reflected by the material, with the blue and purple optical emission of the fluorophore.
OBA’s absorb light in the ultraviolet and violet region (usually 340-370 nm) of the electromagnetic spectrum, and re-emit light in the blue region (typically 420-470 nm) by fluorescence.
This is the electromagnetic spectrum. It starts on the far left with gamma rays and travels to the right through x-rays, microwaves, and radio waves.
The only part humans can see with the naked eye is the visible spectrum above… unless OBAs are involved.
OBAs absorb a portion of the invisible ultraviolet rays and re-emit them as blue light. It’s this reflected blue light that makes fabrics look brighter and whiter.
They are commonly used by commission bleachers and fabric finishers to enhance whiteness and get the fabric to meet the client’s whiteness standards.
However, this is an issue which needs to be dealt with firmly.
Different brands of OBA’s have a large variation of colour reflectivity, and the characteristics of reflection vary from one manufacturer to another and from one concentration to another.
The OBA can invade and distort the Colour Space that the Digital Printer achieves
It therefore follows that if the Colour Space is shifted by an OBA it will distort the actual colour printed by the Digital Printer.
Above all, Fabric for Digital Printing needs to be consistent, and any OBA that is to be used, must be understood, and specified from the outset, as OBA variation is the single largest cause of Print Colour Mis-matches.
It’s easy to detect the presence of optical brighteners under a black ultraviolet light. Fabrics and detergents that contain more OBAs will appear brighter than those with less.
While prints containing different OBAs may appear the same, but they can look different under light sources that contain more UV light.
Manufacturers who assemble outfits using different pieces of printed fabric from different suppliers, can have substantial variation, for although the fabric pieces may match under general light, those colours can shift under UV light sources to give a total colour mismatch.
Manufacturers of the chemicals often specially develop OBA’s to target specific fabric types.
In terms of revenue, the global optical brighteners market is huge and is projected to expand at a CAGR of 4.9% from 2018 to 2026, and is expected to reach US$ 2,036 Mn by 2026 (Transparency Market Research)
This market is driven by the rise in demand in the optical brighteners market in Asia Pacific is estimated to expand at a CAGR of 5.4% during the forecast period, owing to the rapid increase in demand for optical brighteners in the cleaning and textile sectors in the region.
OBA supply is readily available for cellulosic fibres like cotton and synthetic fibres like polyamide.
OBA manufacturers abound, and each product has different emission characteristics, and there is a wide range of compatibility from fibre type to fibre type.
In conclusion, the influence of an OBA on the final colour achieved by the Digital Printer cannot be overemphasised.
If the concentration varies during a run, or the OBA manufacturer is changed from batch to batch, then the profiling that the Printer has previously done on the fabric will be worthless, and he will have to re-profile before he can use it again.
