on overview of cationic curing · • cost efficient sensitization • iodonium...
TRANSCRIPT
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Leading the way
On Overview of Cationic Curing
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Leading the wayApplication areas
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Leading the wayAdvantages of Cationic Curing
•No oxygen inhibition
•Very low shrinkage
• Excellent adhesion
•Dark cure reaction gives high conversion
• Improved coating properties• Increased chemical resistance, hardness etc
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Leading the wayFormulation
Cycloaliphatic Epoxide Main Resin
Onium SaltPhotoinitiator
OxetaneReactive Diluent,Property Modifier
ComponentFunction Products
S105, S128
S130, S140, S150, S160, S170
992, 976, 938, 937, 939
Trade names
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Leading the wayResins: Formulation Base
S105
S128
• Principal resin used in industry• Difunctional cycloaliphatic epoxide• Low shrinkage (ca. 2-4%)• Viscosity (ca. 300 mPa.s @25° C)• Hard polymers • High crosslink density• High Tg
• Difunctional adipate based cycloaliphatic epoxide• Low shrinkage (ca. 2-4%)• Viscosity (ca. 600 mPa.s @25° C)• Increased flexibility over UviCure S105
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Leading the wayResins: Reactive Diluents
O
O
O
OH
S130
S140
• Hydroxy functional oxetane• Low shrinkage • Low viscosity (ca. 8 mPa.s @25° C)• Increased flexibility• Increased adhesion• High cure speeds
• Aromatic oxetane• Low shrinkage • Low viscosity (ca. 8 mPa.s @25° C)• Increased flexibility over UviCure S130• Increased adhesion.
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Leading the wayResins: Property Modifiers
S150
S160
• Aromatic difunctional oxetane• Low shrinkage • Viscosity [ca. 150-220 mPa.s (25°C)]• Toughness, flexibility, thermal stability. • Increased adhesion
• Aromatic difunctional oxetane• Low shrinkage • Viscosity [ca. 240-300 mPa.s (@50°C)]• Hardness, chemical resistance, thermal stability • Increased adhesion
O
O
O
O
n
n=1,2,3
O
O
O
O
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Leading the wayResins Hybrid Crosslinker
O
O
O
S170
• Hybrid Oxetane/methacrylate functionality
• Reduces phase separation in hybrid system
• Adhesion promoter in free radical system
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Leading the wayCationic Photoinitiators
• Generally sulfonium or iodonium salts.
• On exposure to UV light energy produce a strong Brønsted acid.
• The acid initiates the polymerization reactions of epoxy resins, producing a crosslinked film.
• The generated acid remains active and able to initiate polymerisation after UV exposure, known as “dark cure”.
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Leading the wayThe Effect of Anion Nucleophilicity
• Reactivity depends on the low nucleophilicity of the anion.
BF4- < PF6
- < AsF6- < SbF6
- …….B(C6F5)4-
• Hexafluoroantimonate is a very reactive anion.
• Arsenic is toxic and so use is not widespread.
• Hexafluorophosphate is the most common anion used.
• Tetrakis pentafluorophenyl borate anion is extremely fast in silicone epoxys, can be effective in non-silicone media but at a high cost.
Borate ArsenicPhosphate Antimonate Tetrakis Borate
Reactivity
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Leading the waySensitizers in Cationics
• Sensitizer is consumed by the sensitization reaction with the onium salt.
• Very efficient with iodonium salts but less effective with sulfonium salts.
• Typical concentrations 3-4% onium salt, 1% acetophenone, 0.5-1% thioxanthone.
Sensitizer Sulfonium Salts Iodonium Salts
Thioxanthones ✓
Anthracenes ✓ ✓
Benzophenones ✓
Acetophenones ✓ ✓
Titanocene ✓
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Leading the waySulfonium Cationic Photoinitiators
992
976
0
0.5
1
1.5
2
2.5
3
210 260 310 360 410A
bso
rban
ce
Wavelength / nm
S+
S
S+
PF6-PF
6-
• Sulfonium hexafluorophosphate salt• High reactivity• Produces long lived acid species• Low yellowing• Expensive to sensitize.
• Sulfonium hexafluoroantimonate salt• Very high reactivity• Produces long lived acid species• Low yellowing• Expensive to sensitize. 0
0.5
1
1.5
2
2.5
3
3.5
210 260 310 360 410
Ab
sorb
ance
Wavelength / nm
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Leading the wayIodonium Cationic Photoinitiators
937
938
I+
PF6-
0
0.5
1
1.5
2
2.5
210 260 310 360 410
Ab
sorb
ance
Wavelength / nm
• Iodonium hexafluorophosphate salt• Benzene free• Good reactivity• Produces long lived acid species• Low yellowing• Cost efficient sensitization
• Iodonium hexafluoroantimonate salt• Benzene free• Good reactivity• 50% active in glycidyl ether reactive
diluent.• Low yellowing• Cost efficient sensitization
0
0.5
1
1.5
2
2.5
210 260 310 360 410
Ab
sorb
ance
Wavelength / nm
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Leading the wayIodonium Cationic Photoinitiators
939
I+
B-
FF
F
F F
4
• Iodonium tetrakis(pentafluorophenyl) borate salt• Benzene free• Very high reactivity in silicone epoxy systems• Produces long lived acid species• Low yellowing
0
0.2
0.4
0.6
0.8
1
200 250 300 350 400
Ab
sorp
tio
n
Wavelength / nm
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Leading the wayLong Wavelength sensitizers
O
S
O
S
Cl
O
O
S
CPTX DETX2-ITX
Thioxanthones
• Able to activate iodonium cationic photoinitiators to LED light ( 365 – 405nm)• Charge transfer mechanism• Will give some yellowing
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Leading the way
Free Radical Promoted Cationic Polymerisation
• Radicals give redox decomposition of onium salt to produce acid.
• Norrish Type I photoinitiators SpeedCure 73, 84, 2959, BKL, TPO, TPO-L, BPO etc…
Mechanism
Radical Source R.
R.
+ Ph2I+ X-
R+ + Ph.
+ PhI-
UV
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Leading the wayLambson Type I Cationic Sensitizers
O
OH
OOH
O
OH
OOH
P
O
O
O
P
OO
P
OO
O
BPO
84
TPO-L
2959
TPO
73
α Hydroxy Ketones
Phosphine Oxides
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Leading the wayEffect of Water on Cationic Cure
• Water acts as a chain transfer agent, reducing coating physical properties by promoting new chain growth and reducing average MW.
• Mostly surface cure phenomenon.
• Cure speed at 50% humidity is half that at 30% humidity.
• Reduce humidity levels at point of cure to maintain physical properties e.g. hot air blowers
0
200
400
600
800
30 40 50 60 70 80
Cu
re S
pe
ed /
ft
min
-1
Humidity / %
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Leading the way
Effect of Temperature on Cationic Cure
• After activation of the cationic photoinitiator the polymerisation reactions are thermally driven.
• Thermal post curing at will in give very high conversions and resistant coatings.
• Rapid curing speeds reached by increasing temperature using hot air blowers or IR lamps.
0
100
200
300
400
500
25 50 75 100
Cu
re S
pe
ed /
ft
min
-1
Temperature / °C
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Leading the way
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