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

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