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7/24/2019 Intro Basic Uv Curing2012 Mji
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Page 1
Introduction to the Basics of UV/EBChemistry and Formulations
SUNY ESF
Institute for Sustainable Materials andanu ac ur ng
Dr. Mike J. Idacavage
Esstech, Inc.September 27, 2012
Agenda
Introduction to UV/EB Curing
Basic Formulation strategy
Oligomers
Monomers
Photoinitiators
Cationic Cure
Electron Beam
2
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Energy Curable Industrial Coatings
3
Energy Curable Graphic Arts Applications
4
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What is Energy Curing?
Using UV energy, visible light, or high energy electronsas opposed to thermal, evaporative, or oxidative (air-dr cure to form a coatin film or ink
Types of energy used for energy curing:
Ultra Violet (UV): 200 400 nm
Visible light: typically 380 - 450 nm
Electron beam: low energy electrons
5
While I will try to use the term energy curable, please note that the terms radiationcurable or UV/EB curable may be used interchangeably.
Why Use Energy Curing?
Productivity, Productivity, Productivity Seconds to cure vs. minutes or hours
Lower Overall Cost (per cured part) 100% solids, cure speed, recycling of coating, etc
Single component formulas Eliminates mixing errors found in 2 component systems
Regulatory Concerns (VOC emission) Avoid solvent use in most cases
6
Sma er equipment ootprint Less floor space needed
Energy costs (esp. now with high oil prices)
Did I mention Productivity?
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Areas of Strength for EC
Scratch Resistant Coatings (plastic, paper up-grade)
Over Print Varnishes
Printing Inks (Litho, Flexo, Screen)
Wood Coatings
Electronic & Fiber Optic Coatings
Photopolymer Plates
7
EC can generate a high crosslink density network that results in a coating with high gloss and
hardness, scratch and stain resistance and fast cure. EC also works best with flat substrates, which
are found in all of the above markets.
Areas for Improvement
Adhesion to some metals, esp. during post-forming
Adhesion to some plastics
Tear resistance
Low gloss in 100 % solid systems
Low film weight for 100% solids
Overall cure of 3-D parts
8
EC coatings can have high shrinkage, which adversely affects adhesion to non-porous substrates.
Lack of solvent coupled with a fast cure reduces the formulators ability to meet low gloss, low film
build requirements. Additional lamps are needed to cure 3D parts since EC is a line of sight cure
method.
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RADIATION CURING
TYPES OF RADIATION USED
UV - ultraviolet photons
EB - low energy electrons
9
RADIATION CURING CHEMISTRY
Free Radical
Polymerization through double bonds
(Meth)Acrylate double bonds most commonfunctionality
Cationic
Polymerization through epoxy groups
Cycloaliphatic epoxies most commonly used
10
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RADIATION CURING CHEMISTRY
Free Radical Curing - UV Photoinitiator absorbs UV light and generates free
Free radicals react with double bonds causing chainreaction and polymerization
Cationic Curing - UV Photoinitiator absorbs UV light and generates a
ew s ac
Acid reacts with epoxy groups resulting inpolymerization
11
RADIATION CURING CHEMISTRY
Free Radical Curing - EB
Electrons open double bonds initiatingpo ymerization - no p otoinitiatorrequired
Cationic Curing - EB
Electrons decompose photoinitiator to
-for polymerization
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UV CURING
Acrylated Resin(s)basic coating properties
CC
UU
ono unc ona onomer s
viscosity reduction, flexibility
Multifunctional Monomer(s)
viscosity reduction, crosslinking
Additives
UVUV
LightLight
EE
DD
PP
RR
OO
DD
per ormance ine tuning
Photoinitiator Packagefree radical generation
UU
CC
TT
13
EB CURING
Acrylated Resin(s)CC
UU
basic coating properties
Monofunctional Monomer(s)
viscosity reduction, flexibility
Multifunctional Monomer(s)
viscosit reduction crosslinkin
RR
EE
DD
PP
RR
OO
ElectronsElectrons
Additives
performance fine tuning
UU
CC
TT
14
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Formulating for properties
Some desirable properties for coatings:
Adhesion
Cure speed
SARC (scratch & abrasion resistant coatings)
Weatherability
Flexibility
Pi mented s stems
15
Everything You Always Wanted to Know About UVFormulating
16
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Formulation of EC Products
FormulaLamp
17
Application
All three aspects are interrelated
FORMULATING A UV CURABLE SYSTEM
PHOTOINITIATORSPHOTOINITIATORS
ADDITIVESADDITIVES
MONOMERSMONOMERS
OLIGOMEROLIGOMER
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PHOTOINITIATORSPHOTOINITIATORS
FORMULATING A UV CURABLE SYSTEM
ADDITIVESADDITIVES
MONOMERSMONOMERS
OLIGOMER
19
OLIGOMER TYPES
(Meth)Acrylated
Epoxies
Characteristics
fast curing, hard, solvent resistant, lower cost
Aliphatic Urethanes
Aromatic Urethane
Polyesters
flexible, tough, non-yellowing, best weatheringproperties
flexible, tough, lower cost than aliphaticurethanes
low viscosity, good wetting propertiesies
Acrylics
Specialty Resins
good weathering properties, low Tg
adhesion, special applications
20
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Epoxy Acrylate
OLIGOMERS
bisphenol A diglycidyl ether diacrylate
CH2 CH C O CH2 CH CH2 O C
CH3
CH3
O CH2 CH CH2 O C CH C H2
OOHOHO
21
Urethane Acrylate
OLIGOMERS
aliphatic urethane diacrylate
CH2 CH C O R O C NH CH2 NH C O R' O C NH CH2 NH C R O C CH CH3
O OO OOO
CH3 CH3
CH3 CH3
CH3 CH3
22
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FORMULATING A UV CURABLE SYSTEM
PHOTOINITIATORSPHOTOINITIATORS
ADDITIVESADDITIVES
MONOMERS
OLIGOMEROLIGOMER
23
MONOMERS
Monofunctional Monomer
CCHH33 CCHH33
CCHH33
OOCC
OO
CCCCHH22
HH
IBOAisobornyl acrylate
24
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MONOMERS
Difunctional Monomer
O O
TRPGDAtripropylene glycol diacrylate
CH2 CH C O (C3H6O)3 C CH CH2
25
MONOMERS
Trifunctional Monomer
O
CHCHCOCH
CH3 CH2 C CH2 O C CH CH2
O
O
CH2CHCOCH2
TMPTAtrimethylol propane triacrylate
26
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Cure
Speed
Monomer Selection
Flexibility AdhesionVisc.
ReductionResidualUncured
-
Func.
Di-
func.
Trifunc. &
Hi her
27
Like all generalizations, these trends are usually, but not always, true
FORMULATING A UV CURABLE SYSTEM
ADDITIVESADDITIVES
PHOTOINITIATORSPHOTOINITIATORS
MONOMERSMONOMERS
OLIGOMEROLIGOMER
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ADDITIVES
Pigments Flatting Agents
Fillers
Defomers
Wetting Agents
Slip Aids
29
FORMULATING A UV CURABLE SYSTEM
ADDITIVESADDITIVES
PHOTOINITIATORSPHOTOINITIATORS
MONOMERSMONOMERS
30
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Photoinitiators
31
Terms/Glossary
max(pronounced lambda max)
The wavelength at which photoinitiator absorbs the most
energy; also known as peak absorbance
absorbance The amount of light a material takes in as opposed toreflecting or transmitting it
cure The conversion of unreacted material to reacted material;transformation of monomers and oligomers to a polymer
network; in practical terms, usually the point at which the wet
material reaches a mar free state (or any other property of
interest)
photons A quantum of light; a packet of light energy
polymerization The reaction by which monomers (and oligomers) areconverted to high molecular weight materials (polymers)
radical AKA free radical, molecule fragment with 1 unpaired electron.Not an ion (has no charge)
transmission The amount of light passing through a material; the ratiobetween the outgoing (I) and the incoming intensity (Io),
%T = (I/Io) x 100
32
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Why Are PI Necessary?
PI Characteristics Absorb UV light or electrons to form active species (radicals
or acids)
Add to monomer/oligomer to start cure process(polymerization)
Different PI absorb UV light at different wavelengths
Match PI with UV lam out ut
Only reacts with UV-Vis energy, not heat
Long pot life/shelf life
33
Initiation System is irradiated, reactive species (free radicals) created
Pro a ation
UV Radical Polymerization
Oligomers and monomers add to the growing polymer chain,creating a high MW network
Termination Two radicals combine to stop the chain reaction
termination
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Initiation Process
System is irradiated and the photoinitiator absorbs some of
Initiation
the incoming energy
Photoinitiator forms one or more free radicals
A free radical then combines with an acrylate to form a newradical that is the active species for the growing polymer
UV polymerization is line-of-sight only shadowed areas very
35
Propagation Process
Propagation
Free radical
on end of polymer
chain
Reacts with an
acrylate to make a
Referred to as a chain reaction
new radical
36
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Termination Process Two radicals (active species, growing chains, PI fragments)
Termination
If PI concentration is too high, the radicals from the PI cancontribute to a high termination rate
A high termination rate can lead to Greater levels of unreacted material
Poor physical properties (e.g. low adhesion, greater marring, poor
37
Initiation
Summary
I 2 IUV Energy
I + M IM
Propagation
IM + M
IMM + M
IMM
IMMM
P~M + M~P P~M-M~P- -
IMMM + M IMMMM
P~M + I P~M-I
- -
I = Initiator M = Monomer (or any acrylate) P = Polymer chain
38
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Classes of Photoinitiators Photocleavage (unimolecular PI)
a-cleavage PI - Adsorbs light and fragments to form theradicals which initiate polymerization.
Photoabstraction (bimolecular PI)
Hydrogen abstraction PI - Adsorbs light and abstractshydrogen from another molecule (photoactivator) whichproduces radicals.
Amine synergist (photoactivator) - Donates a hydrogen to thep o osens zer o pro uce e ra ca s w c n a epolymerization.
39
Photoinitiator, photosensitizer, and photoactivator are often used as differentwords for photoinitiators even though they are not the same
Liquids are easier to handle in a plant (but often $$)
Photoinitiator Mixtures (liquid blends)
PI blends offer advantages
Absorb over a larger range of wavelengths better chance ofavoiding interference from e.g. pigments and make use ofmore of the available UV energy
40
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Photoinitiator Selection
Absorption characteristics of photoinitiator
and formulated system
Pigmentation
Spectral output of UV lamps
Oxygen inhibition
Weatherability (yellowing)
Handling (liquid vs. solid)
Toxicity
Cost
41
Matching PI with UV lamp
Different UV lamps emit energy in different part of the spectrum
Need to match absorbance of the PI with the output of the lampor ig est e iciency
PI / Lamp Output Match
(Additol CPK / Fusion "H" bulb)
Good absorbance (PI) + Good energy output ("H" bulb) = Good match
42
200
210
220
230
240
250
260
270
280
290
300
310
320
330
340
350
360
370
380
390
400
410
420
430
440
450
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Oxygen inhibition
Oxygen can inhibit (slow down) the cure speed of coatings andinks, especially in thin layers
Solutions:
Amine synergists
Cure under an inert (N2) atmosphere
43
Cationic Cure
44
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CATIONIC CURING MECHANISM
Initiation (Light & Heat)
O
R H+MF 6
-
O
R
H+
O
R
O
R
R
HO
+
initiation
h
photoinitiator
HO
R+
CATIONIC CURING MECHANISM
Polymerization (Chain Reaction; Heat)
polymerization
O
R
O
R
R
HO
+
O
R
R
O
R
R
O
n
+
chain reaction
mO
R
HO
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Radical vs. Cationic
Radical Cationic
wide variety of raw materials more limited raw materialsinhibited by oxygen not inhibited by oxygennot inhibited by high humidity inhibited by high humiditynot inhibited by basic materials inhibited by basic materialsfull cure in seconds full cure in hoursshrinkage - greater shrinkage - lessadhesion - less adhesion - greaterep o cure - grea er ep o cure - ess
cost - less cost - greater
UV/EB market share - 92-94% UV/EB market share - 6-8%
47
UV Cationic Curing
Cycloaliphatic Epoxide(s)
basic coating properties
CU
UV
Light
Polyol(s)
crosslinking, flexibility
Epoxy/Vinyl Ether Monomer(s)
viscosity reduction
Additives
performance fine tuning
ED
PROD
oto n t ator ac agecation generation - commonly sulphonium salts
UCT
48
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Cycloaliphatic Epoxides
Epoxides
Major Component of the formulation
Builds properties of the film
Other components are modifiers
CH2 O C
O
O
49
Electron Beam
50
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ELECTRON BEAM
Ionizing radiation or low energy electrons (e)
have sufficient energy to break bonds in coating, and generate free
can penetrate into and through a coating/ink, and through somesubstrates
are not affected by pigmentation or transparency of coating/ink orsubstrate
generate little to no heat
dose can be precisely controlled
enable high through put
51
E BEAM PARAMETERS
Voltage = Electron Penetration
Equals Thickness Penetrated
units are e volts: MeV, keV
Amperage = Beam Current
Equals Exposure Intensity
units are amps
=
Expressed in kGy (kiloGray) or Mrad (mega rad)
52
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High Voltage E BEAM PENETRATION
10
12
eV
0
2
4
6
8
Voltage,
Penetration, mils
53
LOW VOLTAGE E BEAM PENETRATION
300
350
V
0
50
100
150
200
250
Voltage,
0 5 10 15 20
Penetration, mils
54
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eAND hv PENETRATION
55
LOW VOLTAGE E BEAM
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Thank You!
Dr. Mike J. Idacavage
Director of Business Development
Esstech Inc.
Email: [email protected]
Phone: 1-610-422-6589
57