an overview of free radical photoinitiators · far uv uv c uv b uv a near vis 200-240nm 240-280nm...
TRANSCRIPT
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