An Introduction to Energy Curing

Leading the way

An Introduction to Energy Curing Energy Curing Leading the way • An environmentally friendly technology that uses energy to instantly convert a liquid coating to a cross linked solid coating. • The polymerized cross linked solid coating will have functional and/or decorative properties • Energy sources that are used to cure coatings include electron beam (EB), ultraviolet (UV) or visible light. • The polymerization mechanism of UV curing can be classified into 3 main types, only 2 of which require photoinitiators: • Free radical UV • Cationic UV • Free radical EB – photoinitiators are not required. Ionising radiation. Energy Curing Applications &Benefits Leading the way Markets • Printing inks • Coatings • Adhesive • 3D printing • New application areas Benefits of Energy Curing • No VOC’s • Cold cure/low energy cost • High throughput • Low maintenance costs Ultra Violet Light Leading the way

Light Sources: Mercury lamps - Medium Pressure Mercury Lamp - Doped Mercury Lamps

LED Lamps - 365 nm Image source: - 385 nm Jenton International - 395 nm

Source: Phoseon

Far UV UV C UV B UV A Near Vis 200-240nm 240-280nm 280-320nm 320-400nm 400-450nm Short wave UV Medium wave UV Long wave UV UV-Vis Surface cure High speed Depth cure Depth cure Energy Curing Formulations Leading the way

100% solids formulation

Additives Final adjustment of properties.

Used to start curing. Different PIs will Photoinitiators affect different aspects of the cure.

Monomers and Diluents Viscosity, reactivity, adhesion, migration.

Resins and Oligomers Bulk film properties. Photoinitiator Selection Criteria Leading the way • Absorption • Alignment with the curing lamp spectral output is critical to generate polymerization initiating species. • Desired cure speed • Toxicity and odour. • especially important for applications such as food packaging inks. • Colour contribution to final film - yellowing • Shelf Life Stability • Solubility/Processing • Decomposition Side Products • Cost Free Radical Curing Process Leading the way

Wet formulation applied by rollers, curtain coating or UV Energy Source spray

Dry/cured product

Substrate Direction

What is happening during this process? 1) Photoinitiator absorbs UV light energy creating radicals. 2) Radicals react with acrylate monomers and oligomers inducing crosslinking. 3) Liquid resin system instantly converts to dry/cured product on crosslinking. 4) Polymerization reactions stop immediately on removal of energy (light) source. Types of Free Radical Photoinitiator Leading the way Norrish Type I O O . . OH OH

R Aryl alkyl ketone Benzoyl radical Alkyl radical

When irradiated with UV light energy the photoinitiator cleaves to generate radicals.

Norrish Type II O OH . . CH N(R) 3 2 CH2N(R)2 R R Aryl aryl ketone Amine synergist Ketyl radical Alkylamino radical inert reactive When irradiated with UV light the photoinitiator abstracts hydrogen from a co-initiator (amine synergist) generating radicals. Photoinitiators in Energy Curing Leading the way Far UV UV C UV B UV A Near Vis 200-240nm 240-280nm 280-320nm 320-400nm 400-450nm Short wave UV Medium wave UV Long wave UV UV-Vis Surface cure High speed Depth cure Depth cure

Type I Type II Type I Type II Type I Type II Type I Type II 73 BP 97 PBZ TPO-L ITX TPO-L ITX 84 MBP BDMB BMS TPO DETX TPO DETX XFs01 MBB BPO CPTX BPO CPTX 2959 XKm XKm EMK

Surface Cure Depth Cure Types of Photoinitiator Leading the way Cationic • No oxygen inhibition. • Very low shrinkage. • Excellent adhesion. • Dark cure reaction gives high conversion. • Improved coating properties. • Increased chemical resistance, hardness etc. The Cationic Curing Process Leading the way

Wet formulation applied by rollers, curtain coating or UV Energy Source spray Heat

Dry/cured product

Substrate Direction What is happening during this process? 1) Photoinitiator absorbs UV light energy and produces a strong Bronsted acid. 2) The acid initiates the polymerization reactions of epoxy resins and oxetane reactive diluents. 3) Liquid resin system converts to dry/cured product on crosslinking. 4) Polymerization reactions continue after removal of light energy until acid is consumed. These reactions are thermally driven (Dark Cure) Formulating with Photoinitiators Leading the way

Photoinitiators absorb light energy in order to work. • Curing lamps must emit UV energy in the spectral area that the photoinitiator absorbs.

Anything that can lessen or prevent the absorption of light energy will reduce the amount of initiating species formed. • Oxygen inhibition (Cationic formulations are unaffected by this issue) • Pigments (some colours are more problematic than others e.g. blacks and whites). • Coating thickness

A reduction in initiating species leads to poor curing performance. • Surface tack • Poor through cure • Poor physical properties Benefits of Energy Curing Leading the way

• 100% solids systems No VOC’s, No water evaporation • Cold cure Protects sensitive substrates • High throughput Instant reaction, suitable for continuous processes • Low energy / maintenance costs Reduced energy consumption vs thermally cured coatings. Long lamp service lifetime • Excellent film properties Crosslinked systems provide highly resistant films Leading the way

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