Excimer technology: innovative UV finishing for matt surfaces

Incredibly matt surfaces, pleasing to the eye, pleasant to the touch and resistant to scratches and light: this is what excimer technology and UV finishing make possible. After looking in depth at the benefits of UV LED curing, in this article we explore the new frontiers for the treatment and finishing of flat and raised panels.

These are extremely innovative solutions, and it is no surprise that many, even within the industry, are not familiar with the meaning of the very term excimer.
The first goal of this article is therefore to explain what excimer finishing means. It will then be easier to describe its characteristics and benefits, before reviewing the machines that enable this process.

What excimers are and what “excimers” mean in UV finishing

Etymology first: the term excimer derives from “excited dimer”, that is, an excited dimer, a molecule composed of two sub-units (atoms or simpler molecules) that exists only in an excited electronic state and not in the ground state.

In the context of finishing and, in particular, in curing processes, these molecules are used to create high-quality coated products. How? By means of short-wave ultraviolet (UV) light sources inside a specially designed environment, typically an oven.

Unlike conventional UV lamps, which emit a broad spectrum of UV radiation, excimer lamps produce highly focused monochromatic UV light at specific wavelengths, generally between 172 and 222 nanometres.

When the UV light of an excimer lamp irradiates a liquid lacquer layer, it triggers rapid surface photopolymerisation of the resin, creating a resistant and durable surface. The specific wavelength of excimer UV radiation produces controlled energy transfer, enabling modifications at a superficial level without affecting the underlying substrate.

It is precisely this capability that makes excimers particularly suited to curing processes. With excimer finishing, it is possible to create matt finishes, textured effects, or surface ripples with minimal heat generation.

The machines that exploit this curing technique, in particular UV ovens, are also suitable for evenly matting three-dimensional products, typically doors and panels.

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Excimer technology: benefits and applications in UV finishing

Excimer technology offers several benefits: first of all, it meets the need to reduce energy costs and the environmental impact of processing. This is thanks to the efficiency ensured by short-wave UV curing, which requires limited electricity and does not involve the use of traditional matting agents. In addition, UV lamps generate fewer volatile organic compounds and reduce ozone formation to a minimum. Moreover, the rapid surface curing reduces production times, resulting in lower process and labour costs. 

The high-energy monochromatic UV light of excimer lamps ensures complete curing of the lacquer layer, producing uniform surfaces that are entirely free of gloss or shine.

Then there is the matter of resistance: excimer curing transforms the resins used for coating into fine networks that increase product longevity, protecting them against scratches and chemical aggression. A key advantage for manufacturers of furniture and interior design elements that must combine aesthetics with durability.

More generally, excimer UV techniques are ideal for creating high-end furniture, interior panels, and customised decorative surfaces: the precision of the technology makes it suitable for processing objects with complex designs and structured textures, products where uniform finishing and tactile qualities are a key selling point for end customers.

Excimer finishing process: how it works

So how does the excimer matting process actually work, and what stages make it possible to obtain attractive, durable, abrasion-resistant surfaces without the need for additional chemical agents?

The excimer finishing process consists of several stages, each designed to achieve, as an overall result, a perfectly matt finish with distinctive sensory properties.

Excimer liquid lacquer is usually applied using roller techniques: after being coated, the products are transported into specially designed ovens and subjected to a short-wave UV curing procedure in an oxygen-free environment. This condition is essential, as oxygen would inhibit the curing process.

At this stage, UV photons penetrate the surface of the lacquer: this is the step that triggers the surface curing process of the excimer liquid, which, as it dries, reduces its volume. The rapid exposure minimises heat build-up. The effect is usually the creation of micro-folds of varying thickness, which in turn deform the surface.

The final appearance of the surface depends on the paint formulation and process parameters: this transformation is invisible to the naked eye, but sufficient to deflect light instead of diffusing it, generating a matt visual effect and a very pleasant tactile sensation.

The process ends with the hardening phase of the lacquer layer, usually achieved again by irradiation with a UV dryer.

Excimer oven technology for high-quality matt surfaces

We know that the market increasingly values the sensory aspects of home décor items. The tactile component, in particular, is becoming crucial in choosing furnishings. Soft-touch finishes are therefore gaining prominence: not only do they make contact with the object more pleasant, but they also increase surface resistance to scratches and wear.

To achieve this type of finish, manufacturers need a solution that effectively treats all sides and edges of their products, maximising quality and reducing costs wherever possible. Excimer ovens, capable of processing more complex objects than simple flat panels, are therefore ideal for producing high-quality matt surfaces.

What results do excimer ovens achieve?

Let us be more specific and analyse the results that can be achieved with conventional excimer ovens: the machines, as mentioned, work on flat panels through a short-wave UV curing process in an oxygen-free environment.

To produce high-performance soft-touch surfaces, the lacquer must be treated in such a way as to reach a very high level of mattness, no more than 5 gloss (on a scale ranging from 0 to 100 gloss). This step is essential to achieve another increasingly popular effect, the so-called  "fingerprint-proof" effect: thanks to the light rippling of the surfaces, excimer technology effectively prevents fingerprint marks from forming.

This is exactly what Cefla Finishing’s line allows, dedicated to companies wishing to harness all the advantages of excimer technology.

UV-R: the integrated solution ensuring maximum versatility

UV-R for instance, is a UV curing oven that integrates into a single body all the machine’s elements: conveyor, UV body, and electrical panel. It represents the ideal solution for those seeking versatility and ease of use, without compromising on guaranteed quality of the final result.

Exydry: the future of excimer ovens

For those aiming even higher, there is Exydry, perfect for working on 3D products, which typically must feature matt, resistant edges as well as surfaces. The result of an in-house R&D project, Cefla Finishing’s Exydry is an innovative solution that achieves the matt effect thanks to treatment before full cross-linking, easily reaching values below 5 gloss.

Despite these characteristics, the surface resistance of panels treated and cured in Exydry is extremely high. Furthermore, the nitrogen used to remove oxygen from the X, Y, and Z axes of a shaped panel is significantly less than that required by conventional excimer ovens.

Exydry: How does it work?

With several patented technologies, this innovative system can process, for example, doors coated by oscillating sprayers or robots. The design enables a continuous flow of shaped panels through the oven, removing all oxygen without ever stopping production.
The key benefits, as mentioned, go beyond better finishing quality and the ability to achieve it on three-dimensional objects: they also include reduced production costs, especially thanks to optimised nitrogen consumption.

UV-I: sustainable UV curing with fewer photoinitiators

On the path towards increasingly sustainable finishing, UV-I represents a technological breakthrough. A solution that combines high performance with environmental awareness: UV-I merges UV curing and sustainability.

This innovative oven uses UV curing in an inert environment, significantly reducing oxygen during the curing phase. The result is more efficient cross-linking even with fewer photoinitiators, improving operator safety and reducing the environmental impact of the chemicals used.

UV-I also minimises the use of mercury-containing UV lamps, while maintaining high curing performance. Thanks to controlled use of nitrogen, the process becomes more energy-efficient, bringing tangible benefits in terms of consumption and sustainability.

This technology perfectly matches today’s market needs, offering a compact, safe, and eco-friendly solution, in line with the latest European regulations and the expectations of environmentally responsible companies.

UV iCure: the first mercury-free technology

Finally, still in the field of sustainable innovation, Cefla Finishing’s latest development is UV iCure, the first completely mercury-free UV curing technology, capable of maintaining the same performance as traditional solutions.

The system is designed to comply with European directives on hazardous substances and to effectively replace lamps containing heavy metals, without requiring manufacturers to change the types of lacquers currently in use.

UV-iCure combines excimer and UV LED lamps with optimised wavelengths, in an inert environment, ensuring excellent curing performance without the use of mercury. The absence of fans and the use of water cooling prevent heat transfer to coating and substrate, while the immediate on/off effect reduces start-up times and simplifies system management, eliminating the need for mechanical shutters.

The result is a more compact, safe, and accessible solution compared to electron beam technologies, ensuring top quality and maximum sustainability, making UV-iCure a strategic choice for those wishing to innovate while respecting the environment and regulations.

Learn more on our page dedicated to replacing mercury lamps and in the white paper "From UV-R to UVl LED."

WHITE PAPER: FROM UV-R TO UV LED
A practical guide to replacing traditional mercury vapor UV-R ovens with high-efficiency, sustainable UV LED solutions.