Advancements in shorter wavelength LED technology and its impact on UV curing applications.

Transcription

1 Advancements in shorter wavelength LED technology and its impact on UV curing applications. P.K. Swain, D. Leonhardt, B. Skinner, D. Skinner : Heraeus Noblelight America LLC RadTech Europe 2017, October 2017,

2 Agenda Overview Experimental set up Clear Coat chemistries Irg184, Irg 819 TPO dependence Peak Irradiance vs. Total Dose vs. multiple narrow bands LED vs. Broadband LED vs. Long-wavelength Broadband Recap of prior research Results and discussions Summary/Conclusion Page 2

3 INTRODUCTION Overview/Background UV Curing has been used for many diverse applications Until recently, Hg based UV lamps have primarily been utilized Key Advantages of Hg based lamps: Mature technology Fast process speed (higher UV output) Low cost of ownership Drawbacks: High electrical power consumption Ozone formation Presence of Hg Page 3

4 INTRODUCTION Status of UV LED Technology White light LED manufacturing technology has made steady progress over the past decade Associated manufacturing technology for UV LEDs have benefited Some key benefits of LED technology are: Instant on-off Hg free Longer life Possible lower cost of ownership UV LEDs have shown significant potential for UV curing applications Until now, mostly UV-A LEDs have been used for curing applications Recent emergence of UVC LEDs are expected to bring further innovation Page 4

5 INTRODUCTION Basis of Current Research - I UVLED systems with higher output and flexible working distance have emerged in the market Until now, most existing formulations are optimized for broad band illumination (for Hg based lamps) Since broad band LED sources are not imminent, special formulations, optimized for LED output and wavelength needs to be developed for specific applications Page 5

6 INTRODUCTION Basis of Current Research - II Additionally, exact interactions between LED wavelength, intensity, total dose, formulation s photo-absorption property, curing speed etc. need to be carefully considered for optimum performance In this paper, we would present the curing effect as a function of: (i) LED intensity (ii) process speed (iii) total dose (iv) LED wavelength Page 6

7 EXPERIMENTAL Experimental Set Up - LED Lamp Wavelength, Intensity and Optics 395 nm High density LED packaging High peak irradiance (> 10 W/cm 2 ) Longer working distance LED LAMP OUTPUT IRRADIANCE 30 UVA2 IRRADIANCE (W/cm 2 ) WORKING DISTANCE 5mm 7mm 10mm 15mm 25mm 35mm 45mm 55mm POSITION (mm) Page 7

8 EXPERIMENTAL Experimental Set Up - LED Lamp Wavelength, Intensity and Optics 275 nm Low density LED packaging Low peak irradiance Short working distance Higher driving voltages 4 cm LED LAMP OUTPUT IRRADIANCE Vs. CURRENT Page 8

9 EXPERIMENTAL Experimental Set Up - Hg based Lamp Broadband source (LightHammer 6) Microwave driven electrode-less Standard D bulb Cold reflector (dichroic) 4-6 W/cm 2 Standard conveyor (NO N 2 inerting) Substrates Black and White Leneta cards Page 9

10 UVA2 IRRADIANCE (W/cm 2 ) EXPERIMENTAL Experimental Set Up - Lamps Comparison of custom LED lamp to high power microwave lamp (LightHammer 6) UVA LED: higher peak irradiance over smaller area UVC LED not shown (low scale) 4 cm spatial width Microwave lamp: broader spatial distribution LED at focus LH10 at focus (13mm bulb) LH10 at focus (9mm bulb) POSITION (mm) Page 10

11 DOUBLE BOND CONVERSION (%) DOUBLE BOND CONVERSION (%) DATA & ANALYSIS: CLEAR COATS Review Some Previous Findings (Radtech India 2016) 100 Double bond conversion vs. average power Irg 819 Urethane acrylates Irg nm 385 nm 405 nm July2011 data summary.opj - Irg819 comparison AVERAGE POWER at substrate (W/cm 2 ) Significantly different performance nm 385 nm 405 nm July2011 data summary.opj - Irg184 comparison AVERAGE POWER at substrate (W/cm 2 ) Page 11

12 PhI ABSORBANCE (abs.) & LED EMISSION (rel.) 365 nm 385 nm 405 nm DATA & ANALYSIS: CLEAR COATS Review Some Previous Findings (Radtech India 2016) This can be explained by photoinitiator curves and LED spectrum Irg 819 (4%) Irg 184 (4%) WAVELENGTH (nm) Even for 4% Irg 184, only a small overlap occurs for 365 and 385, but none for 405 nm On the other hand, Irg 819 (4%) has good overlap for all LED wavelengths Wavelength and Shape of the LED emissions curves matter! Page 12

13 Intensity (arb. unit) Intensity, a.u. DATA & ANALYSIS: CLEAR COATS Review Some Previous Findings (Radtech India 2016) Photon Management is Crucial for Monochromaic Radiation Photo-finishing Optimum beam Profile Photo-initiation Photo-initiation 1,00 Photo-finishing 0,75 0,50 0,25 Exposure Time Surface cure 0, l, nm Page 13

14 MAXIMUM CURE SPEED (meters/min) DATA & ANALYSIS: CLEAR COATS Review RadTech 2015 UVA LED v Broadband Lamp Higher concentrations of TPO generally results in better cure when judged by surface tackiness Higher viscosity urethanes cured better with high intensity (25 W/cm2) LED lamps performed better than the broad band Hg lamps with lower intensity (4-6 5% TPO MAXIMUM CURE SPEED v. %TPO Tacky Tack Free TPO (%) Double bond conversion (via FTIR) showed NO correlation with the physical surface tack and therefore only surface tack was considered as a measure of final cure. Page 14

15 ABSORBANCE DATA & ANALYSIS: CLEAR COATS Review RadTech initial LOW VISCOSITY BROADBAND UVA LED v Broadband Lamp 0.30 Inconsistent TPO consumption was observed at lower viscosity, possibly due to increased diffusion and monomers mJ 100mJ Increased absorption at shorter wavelength indicated formations of reaction intermediate (carbonyl containing group) More thorough investigation needs to be conducted for further understanding initial 100 mj LOW VISCOSITY UVA LED mj WAVELENGTH (nm) Page 15

16 EXPERIMENTAL Experimental Set Up Clear Coat Chemistry 1 & 2 CHEM 1 Urethane acrylates EBECRYL 3700 (epoxy acrylate) cp (Low viscosity) EBECRYL 85 (polyether acrylate) CHEM 2 EBECRYL 221 (urethane acrylate) cp (High viscosity) Photoinitiator 5% BASF Lucerin TPO OR Irgacure 184 Synergist: EBECRYL P micron films on white and black cards Page 16

17 MAXIMUM CURE SPEED (M/MIN) DATA & ANALYSIS: CLEAR COATS Maximum cure speed UVA + UVC LED at CHEM 1 (TPO) Maximum cure speed determined by presence of surface tack. 90 CHEM 1 (5% TPO) UVA LED at various peak irradiances UVC LED at 6 mw/cm 2 Multiple 60 mj exposures UVA 6 W/cm2 UVA 10 W/cm2 UVA 20 W/cm2 Cure strongly influenced on BLACK card with UVC exposure (solid line) Cure on WHITE card less affected (Empty Circles) UVC EXPOSURE (mj/cm2) Max Cure Speed per prior work with UVA alone Page 17

18 MAXIMUM CURE SPEED (M/MIN) DATA & ANALYSIS: CLEAR COATS Maximum cure speed UVA + UVC LED at CHEM 2 (TPO) Maximum cure speed determined by presence of surface tack. UVA LED at various peak irradiances UVC LED at 6 mw/cm 2 Multiple 60 mj exposures Cure strongly influenced on BLACK card with UVC exposure (solid line) Cure on WHITE card less affected (Empty Circles) CHEM 2 (5% TPO) UVA 6 W/cm2 UVA 10 W/cm2 UVA 20 W/cm UVC EXPOSURE (mj/cm2) NOTE: 20 & 10 W/cm2 DATA FOR WHITE CARD IS THE SAME VALUE Page 18

19 DATA & ANALYSIS: CLEAR COATS Maximum cure speed UVA + UVC LED using Irg184 CHEM 1 UVC only (mj) UVC (mj) + UVA BLACK card 720 (2) 540 (2) WHITE card 1080 (1) 360 (2) CHEM 2 UVC only (mj) UVC (mj) + UVA BLACK card 360 (4) 360 (4) WHITE card 360 (4) 360 (4) UVA: UVC: single pass 11 W/cm J/cm 2 multiple exposures (# in parens) 6 mw/cm 2 Page 19

20 Improving cure UVA + UVC LED with PhI mixtures CHEM 1 only (Black Card) 2.5% TPO & 2.5% Irg 184 allowed curing with 120 mj UVC (+ UVA) 1% TPO & 4% Irg 184 allowed curing with 180 mj UVC (+ UVA) UVA: UVC: single pass 11 W/cm J/cm 2 multiple exposures (# in parens) 6 mw/cm 2 CHEM 1 5.0% Irg 184 (11 W/cm 2 UVA) UVC only (mj) UVC (mj) + UVA BLACK card 720 (2) 540 (2) WHITE card 1080 (1) 360 (2) Page 20

21 UVC (mj/cm2) Photo Initiator Vs. UVC exposure A possible Tradeoff!!: At 20 M/MIN Line Speed TPO Concentration (%) Page 21

22 Summary of UVA + UVC LED LED wavelength matters as much as total energy Multiple low exposure performs better than one single high energy exposure TPO Curing benefited greatly from low power UVC TPO samples require the lowest total power Irg 184 Irg184 samples could be fully cured with low power UVC For the TPO:Irg184 ratios (1:1 and 1:4) showed marginal improvement Generally, A little UVC (275 nm, 6mW/cm 2 ) goes a long way Full power dependencies (esp. UVC) still need much work Multiple short exposures had better performance than one long exposure Page 22

23 THANK YOU. 23