Leading the way

An Overview of Free Radical Photoinitiators

Leading the wayEnergy Cured Applications

Markets• Printing inks • Coatings• Adhesive• 3D printing• New application areas

Benefits of UV• No VOC’s• Cold cure/low energy cost• High throughput• Low maintenance costs

Leading the wayUV Energy Curing Formulation

Resins and Oligomers

Monomers and Diluents

Photoinitiators

Additives

Bulk film properties.

Viscosity, reactivity, adhesion, migration.

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

Final adjustment of properties.

100% solids formulation

Leading the wayUltraviolet Light

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-VisSurface cure High speed Depth cure Depth cure

Source: Phoseon

Light Sources:Mercury lamps - Medium Pressure Mercury Lamp

- Doped Mercury Lamps

LED Lamps - 365 nm - 385 nm- 395 nm

Image source: Jenton International

Leading the wayFree Radical Curing Process

UV Energy Source

Wet formulation applied by rollers, curtain coating or 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 converts to dry/cured product on crosslinking.

Leading the wayTypes of Free Radical Photoinitiator

Norrish Type IO

OH

R

O

OH. .

Aryl alkyl ketone Benzoyl radical Alkyl radical

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

Norrish Type IIO

R R

CH3N(R)

2

OH

CH2N(R)

2

. .

Aryl aryl ketone Amine synergist Ketyl radicalinert

Alkylamino radicalreactive

When irradiated with UV light the photoinitiator abstracts hydrogen from a co-initiator (amine synergist) generating radicals.

Leading the wayType I: Benzil Ketal

PhotoinitiatorName

Structure

SpeedCure BKL

Features:General purposeShort wave UV absorbance Very fast rate of cleavageHigh thermal stabilitySome yellowing and odour

Applications: Clear and pigmented coatingsAdhesivesStyrene or unsaturated polyester based coatings

O

O

O

0

0.2

0.4

0.6

0.8

1

1.2

1.4

210 260 310 360 410

Ab

sorb

ance

Wavelength / nm

Speedcure BKL

Leading the wayType I: Hydroxyacetophenones

PhotoinitiatorName

Structure

SpeedCure 73

SpeedCure 84

SpeedCure 2959

SpeedCure XFS01

O

OH

OOH

O

OH

OOH

OO

OHOH

Features:Surface cureShort wave UV absorbanceVery low yellowing

Applications: Clear coatingsVarnishesTopcoatsAdhesivesWater based formulations

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

210 260 310 360 410

Ab

sorb

ance

Wavelength / nm

SpeedCure XFs01

SpeedCure 73

SpeedCure 84

SpeedCure 2959

Leading the wayType I: Aminoacetophenones

PhotoinitiatorName

Structure

SpeedCure BDMB

SpeedCure 97

Features:Mid range absorptionDepth and surface cure Sensitized by SpeedCure ITX

Applications: High speed inks ElectronicsEtch resistSolder mask

0

0.5

1

1.5

210 260 310 360 410

Ab

sorb

ance

Wavelength / nm

Speedcure BDMB

Speedcure 97

O

N

O

N

S

O

N

O

Leading the wayType I: Phosphine Oxides

PhotoinitiatorName

Structure

SpeedCure TPO-L

SpeedCure TPO

SpeedCure BPO

SpeedCure XKm

Features:Depth cureLong wave UV absorbancePhotobleachingSpeedCure XKm also has Type II functionality (hybrid)

Applications: Thick coatingsComposites & CIPPTiO2 pigmented coatingsAdhesives

P

O

O

O

P

OO

O

PO

O

O

P

OO

O

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

220 270 320 370 420

Ab

sorb

ance

Wavelength / nm

BPOTPOTPO-LXKm

Leading the wayType II: Benzophenones

PhotoinitiatorName

Structure

SpeedCure BP

SpeedCure MBP

SpeedCure MBB

O

O

OO O

0.0

0.5

1.0

1.5

2.0

210 260 310 360 410

Ab

sorb

ance

Wavelength / nm

Speedcure BP

Speedcure MBB

Speedcure MBP

Features: Economical & efficientSurface cureUsed with amine synergist

Applications: Clear coatsInks

Leading the wayType II: Substituted Benzophenones

PhotoinitiatorName

Structure

SpeedCure BMS

SpeedCure PBZ

SpeedCure EMKFeatures: Mid to long wavelength absorptionSurface and depth cureHigh reactivitySpeedCure EMK can also act as an amine synergist and sensitizer

Applications: Pigmented systemsLED Curing

O

S

O

O

NN

0

0.5

1

1.5

2

2.5

3

210 260 310 360 410

Ab

sorb

ance

Wavelength (nm)

Speedcure BMSSpeedcure EMKSpeedcure PBZ

Leading the wayType II: Benzyl Formates

PhotoinitiatorName

Structure

SpeedCure MBF

Features:Short wavelength absorbanceExcellent surface cureDoes not need an amine synergist Very low yellowing

Applications: Clear coatsWood coatingsWater based formulationsWorks well with PUD’s

O

O

O0.0

0.5

1.0

1.5

2.0

210 260 310 360 410

Ab

sorb

ance

Wavelength (nm)

Leading the wayType II: Thioxanthones

PhotoinitiatorName

Structure

SpeedCure 2-ITX

SpeedCure DETX

SpeedCure CPTXFeatures: Long wavelength absorptionDepth curePhotoinitiator & sensitizerUsed with amine synergistYellowing

Applications: Pigmented systemsLED curingCationic sensitizer

O

S

O

S

Cl

O

O

S

0.0

0.5

1.0

1.5

2.0

210 260 310 360 410

Ab

sorb

ance

Wavelength / nm

Speedcure 2-ITX

Speedcure CPTX

Speedcure DETX

Leading the waySensitizers

Sensitizers work by extending the sensitivity of a PI to longer wavelengths

They absorb light at longer wavelengths than the PI, transfer the energy to the PI and revert to their ground state.

Aminoacetophenone Type I PI can be readily sensitized by thioxanthone or benzophenone derivatives

e.g Speedcure ITX is typically used at between 0.2 and 3% with Speedcure BDMB

Sensitizer Sensitizer * PI * + Sensitizer

h PI

Leading the wayAmine Synergists

Amines act synergistically with Type II photoinitiators and have other important roles such as, oxygen scavenging, solvency and affecting water uptake in ink formulations.

Care should be taken when formulating to avoid acidic environments which may neutralize the amine and inhibit reactivity.

In water-based systems low pH should be avoided as this can reduce the reactivity of the amine synergist.

O

R R

CH3N(R)

2

OH

CH2N(R)

2

. .

Aryl aryl ketone Amine synergist Ketyl radicalinert

Alkylamino radicalreactive

Leading the wayAmine Synergists

Product Name & Chemistry Structure Features

SpeedCure EDB Aminobenzoate Solid.Very fast cure.Suitable for offset litho inks.

SpeedCure EHA Aminobenzoate Liquid, easy to incorporate. Less reactive than SpeedCure EDB. Suitable for flexo inks.

N

O

O

N

O

O

SpeedCure Amine synergists are predominantly based on aminobenzoate chemistry:

Aminobenzoates are much more reactive than simple tertiary amines and exhibit lower “bloom”.

Aminobenzoates are insoluble in water and so are suitable for lithographic applications where water/ ink balance is critical.

Leading the wayFormulating with Photoinitiators

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 radicals formed.

• Oxygen inhibition• Pigments – some colours are more problematic than others.• Coating thickness

A reduction in initiating radicals leads to poor curing performance.• Surface tack• Poor through cure• Poor physical properties

Leading the way

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