Pigment and Inkjet Printing of Textiles and Colour – What is Colour?
Dr K S Murthy (Pidilite Industries Ltd) reports on this SDC EC event which took place at Nirmala Niketan College of Home Science, India
“The Highest Law of Love is Service” is the slogan that defines Nirmala Niketan College of Home Science that was established in 1955. SDC EC in conjunction with the College featured Dr S Y Kamat, Vice President (Industrial Products and Solutions), Kothari Info Tech Ltd, in a lecture on “Advances in Pigment Printing and Inkjet Printing of Textiles” and Mr Yogesh Gaikwad of SDC on “What is Colour” on 28th January 2014 at the College Auditorium, which was attended by a full house of students all specialising in Textiles and Fashion Technology. Despite environmental issues and other problems, pigment printing continues to enjoy the lion’s share of about 50% of the total printing segment because it is fashion oriented, versatile on all substrates, easy and with the lowest water footprint.
Advances in Pigment Printing of Textiles
Dr Kamat spoke on pigment dispersions (1920), synthetic thickeners (1950), printing techniques, fastness properties and aesthetic appeal (1970), German ban (1984) with banned amines released by azo colorants. Representation that pigments are insoluble in water and are not bio-available reinstated azo pigments. Benzidine Yellow and Orange were re-christened as Diarylide pigments freed from benzidine, which was banned earlier. Limits of acceptance set for impurities in pigments led to RSLs viz. banned amines, PCBs, PAH, COC, Dioxin and APEOs. Components of pigment printing system viz. pigment dispersion (prepared from pigment powder with colour indices hue wise by 1960), binder, fixer, synthetic thickener (modified alkali soluble emulsions based on low viscosity polymers), emulsifier and softeners. Binders should not contain acrylamide.
Quinacridone was established with new chemistry. Dyestone Matsui introduced Dyestone X colour, which is neither pigment nor dyestuff prepared by micro-encapsulating technology in polyurethane by mini-emulsion polymerisation (coating of the pigment with a binder for cross linking together) to effect better fastness and softness. Efforts to reduce the cost, softer binders, environmental issues, VOCs, and formaldehyde are the issues for the future.
Inkjet Printing of Textiles
Inkjet printing constitutes 1% of total printed materials and by 2015, it is expected that the digital ink market would become 14% and the key areas are Europe, Brazil and India. In 1970, machines were developed for sampling followed by commercial machines in 1990 and in 2011 Kyocera Japan started inkjet print-heads with exponential speeds. Conventional printers compare production outputs of Rotary or Screen with Inkjet. One requires screens, plates, rollers for transfer of design unlike Inkjet printing. Another aspect is short runs worldwide and the only solution is Inkjet printing. Mass customisation for production of short runs of specific quality. Inkjet is an innovative tool for the designer because it can change designs while printing and colourways. Various terms like Non Impact Printing (NIP), Drop-On-Demand (DOD), Pieco Liter (PL) Lead-Zirconium-Titanium (PZT) and Rastar Image Processor (RIP); essential elements; understanding technology, machinery manufacturers, classification of printers, ink colour gamut, types of inks, software, advantages and disadvantages (disappearing) of digital printing were explained in detail. Inkjet printing entails benefits like substantial savings in time, reduction in water and carbon footprint and better quality of prints etc.
Colour – What is Colour?
Scientists take part in Alan Alda’s Annual Flame Challenge Science contest and answer a vibrant question asked by 11-year-olds from around the country: What is Colour? They can answer the question from their own field — from biology to physics to anthropology or psychology. Does everyone see colour the same way? One of the most classic childhood questions is why is the sky blue? Several colour-centric questions popped up such as ‘How does the brain see different colours’? ‘How do I know that your blue is my blue?’
According to Wikipedia, “Colour is the aspect of things that is caused by different qualities of light being reflected or emitted by them”. A scientist in physics in Hong Kong said that “Colour is the visible spectrum of light.” When you see colour, what do you think of it? The first thing we see is the colour of an object. When it enters your eyes, it goes through your brain and affects the nervous system partly linked to emotion. The colour you see affects your emotion. How does green looks like blue without changing the source of light, pigment and person? Experiences relate to colour reflecting in emotions and that’s why colour is different for every human being.
How does colour exist? What is colour made of? It takes into effect light source, object and observer. When light shines on an object some colours bounce off the object and others are absorbed by it. Our eyes only see the colours that are bounced off or reflected. Can we memorise colour? Colour does not exist outside your brain; it is created by your brain. It is difficult to communicate colour the way we see it. Colour blindness is in red and green areas. 8% males and 0.5% females are colour blind and 10% women have superior colour vision i.e. they see colour in red, orange, green and blue. Factors affecting colour vision include age, anxiety, alcohol, smoking, diabetes etc.
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