Printable Polyester Film Revolutionises Packaging Industry

With a major invention, Uflex Limited has recently hit the packaging industry’s headlines. India’s largest flexible packaging company has managed to find the key to direct UV offset printing on non-absorptive surfaces: a specialty polyester film.

The Initial Problem

The method of direct UV offset printing is gaining in importance in the packaging industry. But until now, polymeric substrates were lacking the crucial characteristic to allow good printing and ink adhesion, making direct printing impossible: an adequate surface energy. To gain optimal printing results on non-absorptive surfaces, however, the surface tension (or dyne level) of the substrate has to be in a certain relation to the surface tension of the ink. And it is important that it is neither too low, nor too high: With a dyne level of the surface lower than that of the liquid, the ink will not wet the surface. With a dyne level of the surface too high, poor wetting and adhesion will lead to poor results. 10 dynes above the dyne level of the liquid is what experts say to be the right amount – but so far, this could only be achieved by a laborious modification of the substrate.

Corona Treatments and Primers: Far From Perfection

In order to make the substrate receptive to direct surface printing, corona treatments or primer coatings were the means of choice, each creating its own challenges: Corona treatments, although cost-effective and fast, can increase static charges in the material treated. Furthermore, they do not protect the created dyne level from loss or decay during, for instance, storage. Applying primer coatings that adhere to both the substrate and the inks, in contrast, is a very elaborate and time-consuming process, impacting convertors’ productivity. In the end, neither process was able to fully meet market’s needs.

Surface Printing Without Treatment

Confronted with these difficulties, Uflex’s assortment expansion must have caused a sigh of relief in the fast-growing flexible packaging industry. After all, Uflex’s specialty polyester film solves all problems at once as it allows direct UV offset printing without any primer or treatment – a big step for e.g. decorative printing and thus packaging. Furthermore, Uflex lists a minimum lead time on the converting end, excellent print results, suitability for high-speed machines and excellent ink adhesion amongst the benefits.

“Convertors had been facing difficulties with primer coating of the films as it takes a lot of time. […] I am happy that the team at Uflex addressed the pain point of convertors by engineering the UV offset printable PET film, which now permits surface printing without any treatment”, says Mr. Ashok Chaturvedi, Chairman and Managing Director, Uflex Limited.

The film comes in bare transparent and metallized variants, where the non-metallized side is used for UV offset printing and UV curing. The metalized version has an optical density ranging from 1.4 to 2.2. The metal bond between the metal and the film is 130-180gms/25mm.

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