Critical photoinitiators for UV-LED Curing: Enabling 3D Printing, Inks and Coatings 150 years E. V. Sitzmann, Ph.D. Radtech UV.EB West 2015, Redondo Beach, CA, March 10, 2015 1
LED (395 nm) curing - Attractiveness 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 2
Application /process selection for UV-LED curing 150 years Application Drop in replacement? Comments / Qualifiers Composites Yes Often better! Slightly longer wavelength compared to UV lasers, and affects PI choices More prone to ambient light poisoning 3D Printing Yes (mostly) May require better stabilizer packages or better shielding Coatings Inks Yes (mostly) Yes Hg lamps use short wavelength type PI for surface curing Need to readjust PI for LED Harder to get speed without inerting Color matching might be more challenging Need some reformulation of resin May need LED + Hg lamp combo s 3
Disecting the reasons why LED (395 nm) curing can (or doesn t) work 150 years 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 O 2 effects & low color after curing is a challenge (especially for UV inks) with LED curing 4
LED (395 nm) curing - Challenges 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 5
Spectral matching of the PI to the UV-LED 6
Spectral matching of the PI to the UV-LED 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 7
BAPO as a two-photon photobleachable photoinitiator 150 years 1st Photon (< 438 nm). BAPO 2nd Photon (< 413 nm). MAPO Higher MW Polymer Acrylate Acrylate Higher MW Polymer 8 Great overlap with LED light, photobleaching enhances optical penetration, and lowers final color
Dry Film Thickness, mil Acyl phosphine oxides: a good fit for LED- 395 nm curing for thick section curing 150 years 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 25 20 15 10 5 0 Exponential Fit: Max cure depth = 23.3 mil, 1/e time = 3.6 min. 0 5 10 15 20 LED Array Exposure Time at Z = 12 mm (min.) 9
Absorbance 150 years Pigment selection cure window Spektren von verschiedenen Flexodruckfarben 3.0 blue 2.5 2.0 1.5 LED Light red yellow black Form. w/o Pigment OPP Foil 1.0 0.5 0.0 200 250 300 350 400 450 500 550 600 650 700 750 Wavelength [nm] 10 Pigments have greater effect on through-cure (Dp) vs. Hg lamps Ease of cure expected to follow %T White > Red Blue > Yellow > Black
ITX + AAK s especially useful for inks O CH 3 C CH 3 S T O CH 3 H 3 C S C N CH 3 O T -cleavage C H 3 S O CH C. 3 C N O.CH 3 E T = 258 kj/mol E T = 256 kj/mol h energy transfer h direct excitation initiation of polymerization O CH 3 C CH 3 S O CH 3 H 3 C S C N CH 3 O ITX can be Type II (H-abstractor), Electron Donor & Energy Transfer Donor 11
Absorbance Photosensitizing cationic photoinitiator (CatS-1) 150 years Cationic curing is not affected by O2 quenching, compared to acrylates Photocuring with LED array (395 nm) is possible using DBA as photosensitizer 1 CatS-1 Irgacure 270 (0.01g/l) DBA (0.01 g/l) O 0.5 O DBA 0 250 290 330 370 410 450 Wavelength (nm) 12
Resin selection - Managing O 2 inhibition 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 13
Conclusions 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 14
References 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 While the descriptions, designs, data and information contained herein are presented in good faith and believed to be accurate, they are provided for guidance only. Because many factors may affect processing or application/use, BASF recommends that the reader make tests to determine the suitability of a product for a particular purpose prior to use. NO WARRANTIES OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE MADE REGARDING PRODUCTS DESCRIBED OR DESIGNS, DATA OR INFORMATION SET FORTH, OR THAT THE PRODUCTS, DESCRIPTIONS, DESIGNS, DATA OR INFORMATION MAY BE USED WITHOUT INFRINGING THE INTELLECTUAL PROPERTY RIGHTS OF OTHERS. In no case shall the descriptions, information, data or designs provided be considered a part of BASF's terms and conditions of sale. Further, the descriptions, designs, data, and information furnished by BASF hereunder are given gratis and BASF assumes no obligation or liability for the descriptions, designs, data or information given or results obtained all such being given and accepted at the reader's risk. BASF Corporation, 2015 15