« Back to In the News

UV LED Curing for Narrow-web Applications

UV LED curing refers to a technique which utilises »energy« output from the light emitting diodes (LEDs) in the Ultraviolet (UV) spectrum to treat inks, coatings, adhesives and other UV curable materials. The energy generated by the UV light triggers the chemical reaction resulting in polymerisation of the material thus hardening (or curing) the material. Traditionally, Mercury-based UV lamps have been utilised for curing, but now more energy efficient and environmentally friendly LED-based UV technology has proven a superior solution to the printing industry.

Replacing traditional lamps Today UV LED curing technology continues to win over many users in the printing world replacing the traditional UV arc lamps. LED curing technology uses semiconductor-based light emitting diodes to project Ultraviolet (UV) light when an electric current is passed through them. When a light-emitting diode is forward-biased, electrons are able to recombine with electron holes within the device thus releasing energy in the form of photons. The colour of the light emitted or corresponding energy of the photon is determined by the energy gap of the semiconductor material. While there are many specific advantages of UV LED lamps, the sum total of the advantages is clear. They provide the following benefits:

● New capabilities to end-users and machine-builders by allowing tighter control over the curing process, especially on heat-sensitive substrates;
● Operating economics include reductions through energy efficiency, low maintenance and long lifetimes;
● Environmental advantages by being ozone- and mercury-free and improving workplace safety. 

Ink formulation for LED technology has evolved significantly in past years and today there are a growing number of suppliers developing flexographic and narrow-web inks which work well with LED technology.

Spectral wavelength 

UV LED lights have a narrow spectral output centred on a specific wavelength, +/– 5 nm. LEDs are a solid-state device; which can be built with various wavelength diodes including but not limited to 395 nm, 365 nm, 385 nm, 405 nm, and 410 nm, unlike the broad spectrum of wavelength range output by Hg-based lamps. This monochromatic distribution (see chart) requires new chemical formulations to ensure proper curing of UV materials (ink). Currently, the most popular wavelength is 395 nm, with 365 nm being used in specific applications.

Ink formulation and materials

Ink formulation for LED technology has evolved significantly in past years and today there are a growing number of suppliers developing flexographic and narrow-web inks which work well with LED technology. LED technology has become more powerful and more compatible inks are available, resulting in substantial advanced capabilities for UV printing. Material suppliers have responded to the demand and challenge in the printing world to formulate raw materials which absorb energy corresponding to output wavelength of UV LED curing units.

One of the key ingredients in the chemical formulation is a photoinitiator which serves as a catalyst to initiate the polymerisation process when exposed to narrow spectrum UV LED energy. With the continued widespread acceptance of UV LED systems, availability of suitable base materials continues to grow. The driving factors in the advancement of chemistry of raw materials is increased capability and cost-effectiveness of commercially available UV LED curing lamps.

Three components of UV LED curing

There are three key components of a UV LED curing system which, when optimised, provide an economically advantageous high throughput solution to the printing industry:
1. UV curable materials (inks) which can absorb energy in the UV region to undergo polymerisation process,
2. UV LED curing lamp which provides energy in the UV region of the spectrum, and
3. a printer where the UV LED lamp is integrated to cure the UV material on various substrates.
These elements together provide a long term sustainable printing method through green technology, eliminating ozone emissions and lowering energy consumption.