critical photoinitiators for uv-led curing: enabling 3d...
TRANSCRIPT
150 years
1
Critical photoinitiators for UV-LED
Curing: Enabling 3D Printing, Inks
and Coatings
E. V. Sitzmann, Ph.D.
Radtech UV.EB West 2015, Redondo Beach, CA, March 10, 2015
150 years
LED (395 nm) curing - Attractiveness
2
What are some key benefits with UV-LED lamps?
Allows low temp curing, since it has no IR output
Potentially more reliable & No Hg!
Potentially less damaging to substrate/colorants
Economically attractive compared to laser light sources for
3D imaging
Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
Application /process selection for UV-LED
curing
3
Application Drop in replacement? Comments / Qualifiers
Composites Yes Often better!
3D Printing Yes (mostly)
Slightly longer wavelength compared to UV lasers, and affects PI choices
More prone to ambient light “poisoning”
May require better stabilizer packages or better shielding
Coatings Yes (mostly)
Hg lamps use short wavelength type PI for surface curing
Need to readjust PI for LED
Inks Yes
Harder to get speed without inerting
Color matching might be more challenging
Need some reformulation of resin
May need LED + Hg lamp combo’s
Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
Disecting the reasons why LED (395 nm)
curing can (or doesn’t) work
4
What are the challenge(s) for developing UV chemistries for curing
with UV-LED lamps?
direct replacement of LED arrays for Hg lamps (or lasers) may
work only for certain applications
PI selection (for optical overlap with lex) is even more critical for
LED curing
O2 effects & low color after curing is a challenge (especially for UV
inks) with LED curing
Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
LED (395 nm) curing - Challenges
5
Other challenge(s) for developing UV chemistries for curing with
UV-LED lamps?
Traditional paradigm of PI blends targeting surface & thru-cure needs
realignment (traditional PI combinations usually do not work)
LED light flux is typically lower
Resin & Modifiers reformulation may be needed
Pigments (interference with optical overlap) might have surprising
effects on curing of coatings
Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
Spectral matching of the PI to the UV-LED
6 Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
Spectral matching of the PI to the UV-LED
7
DBA is a photosensitizer for cationic PI’s
ITX is used “as is” or as sensitizer for
AAK’s
BAPO & MAPO photo-bleach for low final
color
Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
8
BAPO as a two-photon
photobleachable photoinitiator
.
1st Photon
(< 438 nm)
BAPO
MAPO
2ndPhoton
(< 413 nm).
Acrylate Acrylate
Higher MW Polymer
Higher MW Polymer
Great overlap with LED light, photobleaching enhances optical penetration, and
lowers final color Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
9
White UPES Gel Coat (resin: 1718-20-2, 15 wt% TiO2 in XR 1535 + 0.3
pph Irg 819 + 1 pph Irg 184) NB 1718-31
0
5
10
15
20
25
0 5 10 15 20
LED Array Exposure Time at Z = 12 mm (min.)
Dry
Fil
m T
hic
kn
ess,
mil
Exponential Fit:
Max cure depth = 23.3 mil,
1/e time = 3.6 min.
Acyl phosphine oxides: a good fit for LED-
395 nm curing for thick section curing
Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
10
Pigment selection – cure window Spektren von verschiedenen Flexodruckfarben
0.0
0.5
1.0
1.5
2.0
2.5
3.0
200 250 300 350 400 450 500 550 600 650 700 750
Wavelength [nm]
Ab
so
rba
nc
e
blue
red
yellow
black
Form. w/o Pigment
OPP Foil
LED Light
Pigments have greater effect on through-cure (Dp) vs. Hg lamps
Ease of cure expected to follow %T
White > Red Blue > Yellow > Black Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
11
ITX can be Type II (H-abstractor),
Electron Donor & Energy Transfer Donor
Radtech UV/EB West 2015, March 10, Redondo Beach, CA
ITX + AAK’s – especially useful for inks
S
C
O CH3
CH3
C
O
SCH3
CH3
CH3
N O
hh
ET = 258 kJ/mol ET = 256 kJ/mol
direct excitation
-cleavage
initiation of polymerization
T T
energy transfer
C
O
SCH3
C
CH3
CH3
N O. .
S
C
O CH3
CH3
C
O
SCH3
CH3
CH3
N O
150 years
12
Photosensitizing cationic photoinitiator
(CatS-1)
0
0.5
1
250 290 330 370 410 450
Wavelength (nm)
Absorb
ance
Irgacure 270 (0.01g/l)
DBA (0.01 g/l)
Cationic curing is not affected by O2 quenching, compared to acrylates
Photocuring with LED array (395 nm) is possible using DBA as
photosensitizer
O
O
DBA
CatS-1
Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
13
Water-borne >> low viscosity (monomer rich) acrylates
UPES > Methacrylate > Acrylate
Amino acrylate > Ethoxylated multifunctional > Epoxy acrylate
Diluent modifiers: DVE-3 (vinyl ether) at 10% improves photospeed of
acrylated systems when photocuring in air
Thiol terminated oligomeric chain transfer agents – need high purity (to
control odor)
Other additives – certain reactable siloxanes
Cationic/hybrid
Resin selection - Managing O2 inhibition
Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
Conclusions
14
UV-LED curing applications for industrial inks and coating are
growing
The “best” photoinitiator for UV LED curing depends on the
application (in some cases it is a drop in replacement to
conventional UV lamps, in other cases more work is required)
For 390 – 405 nm LED, a good fit is with photobleachable
photoinitiators, like BAPO
Combinations of Type I and Type II photoinitiators or cationic
photoinitiators can help manage oxygen inhibition effects
Radtech UV/EB West 2015, March 10, Redondo Beach, CA
150 years
References
15
K. Davis, “LED Curing versus Conventional UV-curing Systems: Property Comparisons of Acrylates and
Epoxies”, Radtech Europe 2003 Berlin
E.V. Sitzmann, K. Davidson, A. Bendo and P. Vanvolsum, “Photoinitiator selection strategies for thick section
curing of composites and adhesives” , Radtech UVEB West 2007, Los Angeles, CA
E. V. Sitzmann, W. Brunsvold, J. Kazcun “New cationic photoinitiators for electronic, printing and coating
applications “, Radtech UVEB West 2011, Santa Clara, CA
R. Balmer, T. Newsom, G. Shouldice, “Advances in Printing Inks for Alternative UV Sources”, NPIRI Technical
Conference 2013
B. Rundlett, “Developing UV LED Curable Coatings“, Radtech UV.EB East 2013, Syracuse, NY
T. Mawby, “UV LED is Shining New Light on an Old Subject”, NPIRI Technical Conference 2014
Radtech UV/EB West 2015, March 10, Redondo Beach, CA
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