What is UV LED Curing?
UV LED stands for Ultra-Violet light being emitted by Light-Emitting Diodes. UV curing has traditionally been accomplished using mercury-vapor lamps but with the advent of LEDs capable of producing UV radiation, curing devices using LEDs are rapidly finding their way onto the market.
UV curing is a photo-polymerization process that uses UV energy to change a liquid to a solid. Upon absorption of the UV energy, the photoinitiator produces free radicals which initiate cross-linking between resins and cure or solidify the ink or coating.
An increasing number of players in packaging coatings and inks (e.g. overprint varnishes, flexographic printing, digital inks), wood coatings and adhesives (e.g. labels, displays, medical, electronics, industrial) are replacing their traditional mercury lamps by UV LED. Industries beyond those already mentioned are also eager to bring LED curing benefits to their applications. This trend is driven by improvements in process efficiency, economics as well as safety and environmental aspects:
Improved Process Efficiency
- Compact and scalable design of product line
- Instantaneous turning on and off of the curing unit - no warm-up times
- Constant output
- Ease of handling heat-sensitive substrates due to low operating temperatures
Substantial Cost Savings
- Reduced electricity consumption
- Increased lifetime – LED chips last ~30,000 operating hours
- Reduced maintenance
Safe and Environmentally Friendly
- No UVC and UVB wavelengths
- Low operating temperatures
- No ozone emission, no mercury
The allnex star product for UV LED Curing?
UV LED lamps have lower energy and lower lifetime replacement costs, but they can reduce reactivity. To compensate, operations have to slow production speeds and employ high levels of expensive photo-initiators. With its new EBECRYL® LED 03, allnex is offering a solution to these concerns with a low migration resin that provides faster, more complete surface cure while enhancing other properties like adhesion and pigment wetting.
EBECRYL® LED 03 is an acrylate resin that is designed to meet the growing need for better surface cure performance in UV LED-cured overprint varnishes (OPV) as well as flexo and inkjet inks, a need which is not met by current chemistry.
Interested in learning more on this one-of-a-kind innovation, its value proposition and key features?
UV cure with Hg lamps VS. UV LEDs - which is better?
Compared to the output of standard medium pressure mercury UV lamps, which ranges from UVC to infrared wavelengths, UV LEDs emit very intense light in a very narrow range of UVA and visible light wavelengths. As a consequence, the number of useable photoinitiators is limited, and formulations based on them perform well in through-curing but have underperforming surface cure.
Relative intensity of UV light sources (illustrative) ©allnex group
Combining high quality LED lamps with the proper photoinitiator is the first ingredient behind the setting up of a LED curing line. Given the options available on the market at this moment, this needs to be supplemented by the use of specific resins that improve surface curing. In partnership with customers and UV lamp suppliers, allnex has developed a range of resins that covers this need. In combination with the selection of the proper LED machine and photoinitiator, these resins are helping companies to successfully set up UV LED curing systems. In low energy UV curing systems, where the intensity of traditional Mercury lamps is reduced in order to save energy, the same challenges are encountered. As such, below products will also bring solutions for low energy curing systems.
The below resins are exceptionally reactive under LED lamps. Next to conventional performance properties, the selection of resins in a formulation will be based on the balance between high reactivity with low viscosity.
|Functionality||Viscosity (cP @ 25 °C)||Color (G)||Tg (°C)||Tensile Strength (psi)||Elongation at break (%)||Notes|
|EBECRYL® 5781 (bio-based, not available in EU)||2||450||162||1,740||<1||Hard, scratch-resistant, low viscosity and shrinkage|
|EBECRYL® 5850||2||5000||<5||High performing medium viscosity bio-based diacrylate displaying high reactivity with good hardness and scratch resistance
High renewable content (56%)
|EBECRYL® 895||5.5||7,500||Hard, scratch-resistant and high cross-link density|
|EBECRYL® 3703||2||̴ 30,000||57||5,900||47||Amine modified, flexible, good pigment wetting, good chemical resistance.|
|EBECRYL® 3600||2||̴ 20,000||59||12,300||8||Amine modified, high gloss and hardness, low color, excellent chemical resistance|
|EBECRYL® 3418||2||̴ 20,000||4,067||15||High flexibility, gloss, toughness, adhesion and superior chemical and scratch resistance|
|EBECRYL® 8811||2||̴ 450,000||44||1,986||66||Flexible and tough, good abrasion resistance, non-yellowing|
|EBECRYL® 4858||2||7,000||54||5,700||3.5||Low viscosity, good hardness, low color, good impact resistance|
|EBECRYL® 8465||3||2,100 at 60°C||36||3,726||50||High viscosity, tough, excellent exterior durability, non-yellowing|
|EBECRYL® 8210||3.5||4,500||68||6,400||2.1||Low viscosity, low color, high gloss, scratch and abrasion resistance|
|EBECRYL® 4201||4||7,000||12||870||15||Aliphatic, low viscosity, high flexibility and outstanding abrasion resistance|
|EBECRYL® 4501||4||̴ 6,000||9||870||15||Aromatic, low viscosity, high flexibility, high coin and scratch resistance|
|EBECRYL® 1291||6||̴ 80,000||80||1,070||1||High gloss, scratch and abrasion resistance|
|EBECRYL® 2221||6||28,500||49||8,000||3||PETIA-free aromatic, low color, high gloss, hardness, solvent resistance|
|EBECRYL® 5129||6||̴ 20,000||30||9,100||4||Flexible, high gloss, good scratch and abrasion resistance|
Regulation friendly for tin, heavy-metals* and quinones *As defined by C.O.N.E.G’s Toxic in Packaging Legislation, the ASTM Standard Consumer Safety Specification on Toy Safety F 963 (ASTM F 963-08), or the EU Directive 94/62/EC (and amendments) on packaging and packaging waste
The use of following diluents to reduce viscosity will contribute to increased reactivity under LED curing.
|Functionality||Viscosity (cP @ 25 °C)||Notes|
|EBECRYL® 110||1||̴ 20||Excellent viscosity reduction and flexibility|
|EBECRYL® 130||2||160||aliphatic di-acrylate, increases Tg of formulation|
|EBECRYL® 160||3||80||Good flexibility while retaining hardness|
|EBECRYL® 85||3.6||̴ 160||Amino modified polyether acrylate, giving low odor and high gloss. Recommended for low migration applications.|
|EBECRYL® 45||4||160||Polyether acrylate, improves hardness and solvent resistance of formulation. Recommended for low migration applications.|
|EBECRYL® 892||4||̴ 140||Polyester acrylate, giving low odor and high surface hardness|
Our waterborne UV resins
The allnex UCECOAT® range of waterborne UV resins is very well suited for LED curing. Waterbased systems will inherently reduce oxygen inhibition, and because of that display improved surface cure. Additional information on such systems can be found here [ADD NEW LINK]. Within allnex UCECOAT® range of waterborne UV resins, UCECOAT® 7200 stands out for its high reactivity.
|Solid Content||Viscosity (cP @ 25 °C)||pH||Notes|
|UCECOAT® 7200||65||<700||3-5||High solid content, high scratch, abrasion and chemical resistance. Can be combined with EBECRYL® P115 as neutralizing amine and as LED booster.|
|UCECOAT® 7210||65||<1,000||2-5||High solid content, recommended as blending partner for UCECOAT® 7200 to adjust flexibility|
Our LED Boosters
The following LED boosters can be added to improve surface cure. These additives will mitigate oxygen inhibition to improve surface cure.
|Functionality||Amine content (meq/g)||Viscosity (cP @ 25 °C)||Color (G)||Recommended levels in formulation||Notes|
|EBECRYL® LED 02||2.3||450||<1||25%||Mercapto modified polyether acrylate; Used as a co-binder to increase surface cure
|EBECRYL® LED 03||2||3.0||450||<1||5-15%||Polymeric amino modified polyether acrylate; used to increase surface cure, while enhancing adhesion to different plastic substrates, and with no detrimental effect on color strength in inks and a minimal impact on rheology.
|EBECRYL® P115||0||4.2||~20||<2||5-10%||Reactive amine additive used in place of more fugitive amine synergists to increase surface cure|
|EBECRYL® P116||0||4.2||~20||<2||%||Reactive amine additive used in place of more fugitive amine synergists to increase surface cure|
|EBECRYL® 7100||2||2.5||~1200||<4||5-20%||Oligomeric amine modified acrylate functional resin, generally used as an additive or diluent for more viscous oligomers. Accelerates surface cure, & promotes adhesion to different plastic substrates|