Transcript
TECHNOTES
NARROW WEB
UV LED – the time is now... UV LED is an alternative curing technique to mercury curing which is primarily used today to cure UV inks in the narrow web industry. Used already in many industrial applications, such as visible lighting, water purification, and nail curing, this technology has now crossed over into printing applications. It is now starting to be used regularly in UV inkjet, large format UV screen and UV sheetfed applications also.
A LED lamp has a very narrow wavelength, with a peak around 395nm only. Although LED lamps are available with alternative wavelength diodes including 375nm, 395nm, 405nm and 410nm, etc. (±20nm). Therefore the ink and coating technology must be reformulated so that the reactivity and cure results are similar but with the high intensity LED output. Wavelength Comparison
UV LED is an abbreviation for UltraViolet Light Emitting Diode. It offers significant advantages over mercury curing.
UV curing with a LED lamp occurs exactly the same way as when using a standard mercury lamp. The ink, coating or adhesive when exposed to the UV lamp causes a polymerization reaction to occur. A free radical curing UV Flexo ink consists typically of the following raw materials, where each ingredient gives certain properties to the finished ink: Component
Function
•Pigment
Colour shade, strength & light fastness
•Oligomer
Binder - Adhesion properties & pigment wetting and press performance
•Monomer
Diluent - viscosity, cure rate & adhesion
•Photoinitiator Reactive ingredient to start polymerization, cure properties & odor •Additives
Stabilizers & flow agents
Any UV curing ink will only cure when it is exposed to UV light. In this case, the oligomers and monomers react with the photoinitiators and a crosslink reaction begins. If there is not enough light, only surface cure will be achieved, which can result in poor adhesion. The choice of pigment will affect the choice of photoinitiators, as they will compete to absorb the UV light.
Formulation for LED curing The main difference between a standard mercury lamp, and a LED lamp is the wave lengths emitted from the lamps which are available for curing to take place. A standard lamp has a broad spectra of wavelengths which spread from UV-A through UV-B and UV-C and visible and infrared. This means that an ink or coating formulation will have a mixture of photoinitiators to allow the produt to achieve optimum cure.
395 LED
Relative Intensity
Curing mechanism
Mercury Lamp
Wavelength (nm) UVC
UVB
UVA
VISIBLE LIGHT
INFRARED
100-280nm
280-315nm
315-400nm
400-700nm
700-1800nm
Photo courtesy of Phoseon Technology Traditional UV inks will not cure adequately with UV LED lamps
Formulation considerations: When creating a robust UV LED system, the formulation of the ink/coating is, in many respects, even more critical to success in creating a good cure rate than the light source selection. Cure rate is a function of not only the amount of UV energy, but also how well matched that UV energy is to the spectral response of the photoinitiator used in the formulation. But it doesn’t stop there; the photoinitiator is just one small component of the material, which also contains oligomers (pigments) and monomers. In fact, the photoinitiator makes up only a small percentage of the UV system (typically 0.5-10%). The photoinitiator or photoinitiator blend plays the pivotal role determining the cure rate, but oligimer and monomer selection are also important factors. EkoCure, UV LED ink-technology is based on a carefully selected combination of newly developed photoinitiators, and work with a range of UV LED light sources.
UV LED Print Guide LED lamp advantages There are many advantages to using LED lamps. These can be split into economical and environmental advantages. Economic/Productivity/Expanded Capability Advantages: • Press UPTIME – less equipment faults, presses run longer and without lamp faults, higher certainty of cure with inks from process. • Faster cure/higher productivity – better UV curing allows for faster speeds and more combination printing. • Energy Efficient – UV LED lamps require ~ 50% less energy thereby saving money. • Long Lifetime & Low Maintenance – UV LED lamps last over 20,000 – 50,000 hours of run time as compared to a mercury lamp running ~2,000 hours total time; less labor/ maintenance. • Solid State: Instant on/off – there is no waiting for lamps to heat up or cool down saving valuable press time. • Expand the capability of the press by running heat sensitive/ thin films on a press without heat management. A LED lamp does not have infrared and thus does not create heat as mercury lamps do. • UV LED lamps are very compact and flexible and can easily be adapted to any press platform. • UV LED systems are smaller and don’t require large blowers to move air, etc and thus take up less space in production area making room for more equipment. Environmental & Safety Advantages: • Removes toxic mercury from the process and thus no need to deal with hazard waste disposal of lamps. • Removes ozone generation since there is no UV-C light output from lamp – ozone is a respiratory hazard and pollutant.
This provides advantages to cure thicker films (such as screen printing) and darker more opaque colours (such as blacks and opaque whites). This will enable printers that are doing combination printing to print faster speeds with more assuredness of cure and adhesion.
Lamp & Press Suppliers of LED Many lamp and press manufacturers are working and can provide UV LED lamps and UV LED presses. However not all lamps are the same! Lamps can differ in the wavelength output as well as the peak irradiance output amongst other parameters. Flint Group can help you select the proper lamp specifications for your application needs. Press suppliers will offer new presses or retrofit an existing press.
The Future of UV LED printing is NOW! Flint Group provides a range of products for LED curing under the EkoCure™ brand name. ▶UV ▶ LED High Performance Flexo and Rotary Screen Inks, Coating & Adhesive TECHNOLOGY WHICH OFFERS THE MOST INNOVATIVE, SUSTAINABLE, AND VALUE ADDED PRODUCT INTRODUCTION IN OUR INDUSTRY TODAY! ▶These ▶ inks will be the first commercially available inks designed for flexo and screen combination print formulated specifically for UV LED curing. EkoCure™ brand will cover a full range of inks: EkoCure™ F (UEF): • UV LED UV Flexo system • Available in a full range of colours and pigment selection EkoCure™ SN (UEN):
• Lamps are not hot to touch and thus are safer.
• UV LED UV Rotary Screen Opaque Whites
• Systems are much quieter, less noise pollution.
• UV LED Rotary Screen Colours
• Safer cleaning and maintenance (very little required) and thus less risk of injury. • The bright blue light emitted from the UV LED lamps is not recommended to look at, but unlike standard mercury light it will NOT cause permanent eye damage. Note – we still recommend use of safety glasses that filter UV light.
UV Flexo Coatings (UEV) (gloss, matte, TTR, Cast and Cure) & Primer UV Lamination/PSA and Cold Foil Adhesives (UEH) UV EBONY Black –density >2.0 UV Flexo Shrink Whites (high and low COF) – (UEF) UV Flexo Metallics (silver and gold range) – (UEM)
UV LED light with its high peak irradiance, and UV-A and visible light emission, provides a deeper penetrating light source.
For more details on UV LED printing, call your nearest Flint Group Narrow Web office or dealer. T +1 763 559 5911 Toll Free in the U.S.(0800) 328 7838 F +1 763 559 3725
[email protected]
Any products which are available for traditional UV curing today can be converted to this technology!
The aim of our technical documents is to inform our customers about general values. However, the transferability of general values known from experience and laboratory results to concrete practical applications depends on a number of factors which are beyond our control. We therefore ask for your understanding that this advice document cannot be used as the basis for claims in law. Furthermore, the correct application for each product has to be checked carefully for suitability. For application details refer to Technical Data Sheet. Product names followed by ® are trademarks registered by Flint Group Incorporated.
Version: 08.14.2014
Deeper Curing with LED
Flint Group Narrow Web 15500 28th Avenue North, Plymouth, MN 55447, USA www.flintgrp.com
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