Sustainable Industry: experimenting with UV Printing technology in Fashion

The Fashion industry has always been one of the sectors with the greatest environmental impact.

Traditional textile printing processes involve the use of highly polluting chemicals, which are difficult to dispose of, and the consumption of considerable amounts of energy and water.

In traditional industry, the problem of customising a fabric — by printing patterns, decorative motifs or simple labels — sees in screen printing the almost universal solution, regardless of the type and nature of the material used.

Screen printing entails the use of large amounts of materials to produce the frames or screens, the use of chemically aggressive inks, the abundant consumption of water in the washing phases and the production of numerous waste materials due to the wear of the screens and their disposal.

A correct, environmentally respectful management of the screen-printing process necessarily entails an increase in production costs, with the consequent risk of having operators that work in violation of the rules and in unfair competition with more virtuous companies.

In the digital era, a partial alternative to screen printing comes from the “ink-jet” sector. On the market there are plotters capable of either direct printing on fabrics or indirect printing through sublimation-ink technology.

The main problem of these more recent technologies lies in the limited range of materials that can be printed.

Industrial Ink-Jet printing is usually carried out using solvent-based inks. The print heads literally spray onto the material to be decorated the pigment dissolved in a chemical solvent whose purpose is to favour the chemical reaction that allows the colour to bond with the molecules of the material before evaporating.

The materials capable of binding the pigment are exclusively synthetic and mostly made of vinyl-based polymers.

In recent years, in the Chirale laboratories we have experimented with and developed processes capable of ensuring direct Ink-Jet printing on a very wide range of materials, achieving good results even with materials based on natural fibre.

In some cases these are highly artisan techniques; in other cases the process lends itself to industrialisation.

While this line of research has the advantage of allowing companies to use a consolidated, low-cost technology, it still has limitations that put restrictions on the creativity of the style offices of Fashion companies.

A more promising technology, capable of offering an almost universal solution, is UV Printing. What is it about?

UV Printing is a technology derived from ink-jet printing. In fact, in this case too, piezoelectric print heads are used, capable of spraying tiny droplets of an emulsion containing colour pigments at high speed.

The difference lies first of all in the chemical compound used to carry the pigment. In traditional Ink-Jet printing the pigment is dissolved in a solvent; in UV Printing the pigment is suspended in an emulsion whose diluent is the precursor of a photopolymer.

Photopolymers are those materials in which the polymerisation process takes place when energy — in the form of light radiation — is supplied to the resin containing the mix of base molecules (monomers) that will later aggregate into the chains forming the final material.

The heads of a UV printer spray tiny droplets of resin containing the pigments, which are deposited on the printing substrate. On the print head, on either side of the piezoelectric heads, are placed high-power UV LEDs that radiate light in the ultraviolet range onto the droplets just deposited on the substrate, causing them to polymerise.

The pigments are then incorporated into tiny bubbles of material we may improperly call “plastic”. The micro-bubbles strongly adhere to the substrate by virtue of mechanical bonds due to the microscopic roughness of the material.

In effect, UV Printing is capable of fixing colour onto any material that is not strongly water-repellent. It is a universal printing process for almost any kind of substrate, with very few exceptions.

The range of materials on which UV Printing can be applied can be further extended through the use of dedicated primers. A primer is a chemical compound spread between the substrate (the material to be printed on) and the emulsion containing the colour pigments. The primer thus acts as an additional layer that on one side bonds chemically with the substrate and on the other mechanically binds the micro-bubbles containing the pigment.

It is therefore clear that this technology allows printing on any kind of material, on a par with — if not even more than — the traditional screen-printing technique. Besides being a lower-environmental-impact solution, it also has other advantages. Let’s see why.

• The UV Printing process is more eco-sustainable since it produces no industrial waste and does not consume water resources, as it is not necessary to clean accessories and tools, contrary to screen printing.
• The latest-generation UV inks are low-environmental-impact and far less toxic than screen-printing inks, since adhesion happens through the mechanical bonds created during the polymerisation phase of the droplets containing the pigment, and not through chemical adhesion to the fibres or to the substrate. There is no solvent evaporating into the environment.
• The process is entirely digital. From the 2D files containing the texts and images to be printed, the workflow goes directly to the printing phase without having to produce matrices or other intermediate tools. The process is in every respect a digital printing process.
• Colour management and graphic possibilities are those typical of modern digital printing and much more controllable in terms of resolution and gamut compared to screen printing.
• Each layer of a UV-technology print, unlike Ink-Jet where the solvent evaporates, has a thickness of a few microns. By overlaying multiple layers, it is possible to control precisely and selectively the thickness of different parts of the images, giving them a 3D relief, making it possible to create tactile patterns and textures (for example orange peel, leather, reptile scales, …).

Our R&D Centre, FabLab Ostiense, has recently been enhanced with the installation of a flatbed UV printer, specifically commissioned from Roland DG.

It is an industrial-class machine, derived from the commercial Versa UV LEC 330 plotters, equipped with a printing bed of 760 mm x 1,500 mm with a dual pneumatic function — vacuum suction to hold the substrate during processing, and an air cushion to facilitate the positioning of even very heavy substrates in crystal, stone or metal.

The cartridge set has been specifically configured to include, in addition to the classic four-colour-process inks, white to allow printing on dark or transparent substrates, glossy for finishing and 3D-relief effects, and a primer. This last element allows primer management at the level of each individual image pixel, minimising environmental impact and including this pre-treatment within the digital workflow.

The new technology is already available to all our customers from 3 January 2022. The first experimentations in the context of the first two pilot projects were started last December.