Highly efficient UVLED curing process with IR irradiation

Heraeus K.K. Noblelight DivisionKazuo Ashikaga & Kiyoko Kawamura

IntroductionRadical curing system irradiated by LED

Direct irradiation (excitation) system to photoinitiatorSensitized initiation system

IR plus LED hybrid irradiation process in radical curing systemCationic curing system

Sensitized cationic curing system IR plus LED hybrid irradiation process in sensitized cationic curing systemSummary

Table of contents

RadTech 2018 Technology Expo & Conference | Kaz Ashikaga | May 8, 20182

Curing reaction systems examined by 395nm LED irradiation

RadTech 2018 Technology Expo & Conference | Kaz Ashikaga | May 8, 20183

Direct irradiation (excitation) Sensitized irradiation

O

O

C

C

O

O

DOOA

Sensitizer

Radical initiator Cationic initiator

TPO

HCPK (184)

DMDPE (651) HMPP (1173)MPEA (AM-90G)

Resin system

IMMPH (250)

Initiator

R O CO

CH

CH2

OCO

HC

H2C n

Polyester acrylate (M-8100)

Epoxy resin (828)Eeq: 184

BP

I+ CH2CH(CH3)2H3C

PF6-

CH2 O CH2 CH CH2

OOCH2CHCH2

O

hP

OO O

P

O*3

P

OO

Photo-cleavage reaction of TPO

4

0102030405060708090100

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

300 320 340 360 380 400 420 440 460 480 500R

elat

ive

Inte

nsity

Abso

rban

ce

Wavelength(nm)TPO Abs LED

TPO absorption and LED395nm emission spectra

Good spectra matching between TPO absorption and monochromatic LED395nm emission

RadTech 2018 Technology Expo & Conference | Kaz Ashikaga | May 8, 2018

Highly reactive and sensitive to oxygen

inhibition

0 500 1000 1500 2000 2500 3000 3500Iradiation enegry (mJ/sq.cm)

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Substrate: 100μmPET film Coating thickness: 10μm Formulation: HDDA/LR9029 = 40/60UV condition: LH10 H-bulb Stepwise irradiation: every 100, 200, 500 and 1,000mJ/cm2

TPO: BASF Irgacure TPO

TPO Energy

2%

100x4 pass200x10 pass500x6 pass1000x3 pass

4%

100x2 pass200x2 pass500x6 pass1,000x3 pass

6%100x2 pass

200x２pass500x2 pass1,000x2 pass

Curing behavior in TPO initiation system observed under step-wise irradiation

Curing behavior by step-wise LED irradiation

• Tack free surface could be easily obtained by every 100mJ/cm2 stepwise irradiation• Every 1,000mJ/cm2 irradiation did NOT provide tack free surface ⇒ No cure!

Observations

Not curedNot cured

Not curedNot cured

Continuous or intermittent LED irradiation in TPO system

6

0

10

20

30

40

50

60

70

80

0 500 1000 1500 2000 2500

Conversion

 (%)

Irradiation energy (mJ/sq.cm)

20msOn150msOff continuously On

continuousIrradiation

Time (msec)

Time (msec)

IntermittentIrradiation

20ms 20ms150ms 150ms

Acrylic double bond conversion (M-8100 w/4%TPO)

Tack free surface

Tacky surface

20ms irradiation with 150ms dark time170ms interval irradiation

Normal lamp on irradiation

Almost same double bond conversions were obtained by both continuous and intermittent irradiationsTack free surface was provided byonly intermittent irradiation

RadTech 2018 Technology Expo & Conference | Kaz Ashikaga | May 8, 2018

GPC analysis for obtained polymers

7

(methoxy polyoxyethlene acrylate)AM-90G from Shin-nakamura Chemical

0

1000

2000

3000

4000

5000

6000

7000

8000

0 1000 2000 3000 4000 5000

Mn

Irradiation Energy (mJ/sq.cm)

20mOn-150mOff Continuously On

0102030405060708090

100

0 1000 2000 3000 4000 5000

Poly

mer

con

vers

ion

(%)

Irradiation energy (mJ/sq.cm)

20mOn-150mOff Continuously On

Polymer conversion

Photo-initiated polymerization of mono-functional monomer

Number average molecular weight (Mn)

Polymer conversions are almost same against irradiation energy for both irradiation systems

Mn for polymers provided by continuous irradiation is almost constant against irradiation energyMn for polymers obtained by intermittent irradiation is increased with increasing irradiation energy

RadTech 2018 Technology Expo & Conference | Kaz Ashikaga | May 8, 2018

Storage modulus changes against double bond conversion

8

0102030405060708090100

0

100

200

300

400

500

600

700

0 10 20 30 40 50 60

Con

vers

ion(

%)

G'

G"

Energy(mJ/cm2)G' [Pa] G'' [Pa] Conversion

0102030405060708090100

0

100

200

300

400

500

600

700

0 10 20 30 40 50 60

Con

vers

ion(

%)

G'

G

"

Energy(mJ/cm2)G' [Pa] G'' [Pa] Conversion

FT-IR

Rheometer

UV-LED

Fiber cable from UV-LED

to cone

Intermittent irradiation Continuous irradiation

Storage modulus and double bond conversion are increased with increasing irradiation energy by intermittent irradiation

Little storage modulus change was observed by continuous irradiation, even under high double bond conversion

Real time measurements of double bond conversion and rheology changes by LED irradiation

RadTech 2018 Technology Expo & Conference | Kaz Ashikaga | May 8, 2018

What happens, when TPO is irradiated by LED?

9

hP

OO O

P

O

P

OO

>360nm

Initiation and propagation reactionsO

P

O

or MM

Rapid radical coupling with diphenylphosphonoyl radical to terminate propagation reaction

P

O

P

O

M +

Photo-cleavage reaction

Secondary cleavage reaction is induced by shorter wavelength UV (< 360nm) irradiation,to reinitiate polymerization in case of mercury lamp irradiation

P

O hP

O

M + M M+

Rapid recombination in highly viscous media

Major termination process by steady LED irradiation

Ex. Mercury lamp irradiation

RadTech 2018 Technology Expo & Conference | Kaz Ashikaga | May 8, 2018

<360nm

Pre-IR plus UVLED hybrid irradiation for TPO initiation system

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UVLEDPre-IR

0

20

40

60

80

100

0 500 1000 1500 2000 2500

Conversion

(%)

Irradiation Energy(mJ/cm2)UV‐LED Only PreIR+UV‐LED

Double bond conversion against irradiation energyin TPO initiation system

Schematic lamp layout for Pre-IR plus UVLED

0 1 2 3 4 5a.u.

Wavelength(μm)

Emission spectrum of carbon emitter

0

20

40

60

80

100

120

0 20 40 60 80

Tempe

rature(deg.C)

Linespeed(m/min)1.6kW 3.2kW 6.4kW

Film temperature against linespeed

IR: Carbon IR CZB2000/300GSubstrate: 100mmPETEquipment: radiation thermometer• Higher double bond conversion (ca.15%) was provided

by pre-IR irradiation

• UV curable materials are activated by IR irradiation before UVLED irradiation

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Minimum energies for curing in intermittent/preIR plus UVLED irradiations

UV-LED Irradiation period Dark period UV-LED Irradiation period w/preIR

• Intermittent irradiation by LED is efficient to reduce the minimum curing energy and process time• The minimum energy for curing is remarkably reduced by pre-IR irradiation for both continuous and intermittent irradiations• Total process time for curing can be shortened by pre-IR irradiation• Intermittent irradiation process is still effective to reduce required irradiation energy for curing• Shorter LED emission time during intermittent irradiation provides more advantages to reduce total energy for curing• Emission time and total process time should be balanced in intermittent irradiation process

0 100 200 300 400 500 600 700 800 900 100011001200

50on/150off

40on/150off

30on/150off

ContinuouslyON

Process time(msec)

M8100/AM90G/TPO=60/40/6Minimum 

required energy(Maximum speed)

10160mJ/sq.cm(1m/min)

195mJ/sq.cm(3m/min)

278mJ/sq.cm(4m/min)

399mJ/sq.cm(4m/min)

0 100 200 300 400 500 600 700 800 900 100011001200

PreIR+50on/150off

PreIR+40on/150off

PreIR+30on/150off

PreIR+Continuously ON

Process time(msec)

M8100/AM90G/TPO=60/40/6 Minimum required energy(Maximum speed)

508mJ/sq.cm(20m/min)

97mJ/sq.cm(5m/min)

185mJ/sq.cm(6m/min)

215mJ/sq.cm(9m/min)

UVLED Pre-IR Plus UVLED

IR output: 3.2kW

Sensitized phenyl ketone initiation system

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O

O

C

C

O

O

+

Sensitizer Photo-initiator

Initiation species

Emission spectra of UVLEDs and absorption spectrum for sensitizer and initiator

9,10-Dioctanoyloxy anthracene HCPK

Double bond conversion with and without pre-IR irradiations in M-8100 system

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0 400 800 1200 1600 2000 2400 2800

50on/150off

40on/ 150off

30on/ 150off

Continuously ON

PreIR+Continuously ON

Process time(msec)

M8100/AM90G/184/581=60/40/8/1 Minimum required energy

1270mJ/sq.cm(8m/min)

4064mJ/sq.cm(2.5m/min)

>1170mJ/sq.cm(<0.5m/min)

1588mJ/sq.cm(0.7m/min)

2280mJ/sq.cm(0.7m/min)

0 400 800 1200 1600 2000 2400 2800

50on/150off

40on/ 150off

30on/ 150off

Continuously ON

PreIR+Continuously ON

Process time(msec)

M8100/AM90G/BP/581=60/40/8/1 Minimum required energy(Maximum speed)14538mJ/sq.cm(0.7m/min)

16961mJ/sq.cm(0.6m/min)

>1170mJ/sq.cm(<0.5m/min)

>2224mJ/sq.cm(<0.5m/min)

>3192mJ/sq.cm(<0.5m/min)

0 400 800 1200 1600 2000 2400 2800

50on/150off

40on/ 150off

30on/ 150off

Continuously ON

PreIR+Continuously ON

Process time(msec)

M8100/AM90G/651/581=60/40/8/1 Minimum required energy(Maximum speed)

1270mJ/sq.cm(8m/min)

2540mJ/sq.cm(4m/min)

834mJ/sq.cm(0.7m/min)

926mJ/sq.cm(1.2m/min)

938mJ/sq.cm(1.7m/min)

0 400 800 1200 1600 2000 2400 2800

50on/150off

40on/ 150off

30on/ 150off

Continuously ON

PreIR+Continuously ON

Process time(msec)

M8100/AM90G/1173/581=60/40/8/1 Minimum required energy(Maximum speed)

5976mJ/sq.cm(1.7m/min)

6773mJ/sq.cm(1.5m/min)

>1170mJ/sq.cm(<0.5m/min)

>2224mJ/sq.cm(<0.5m/min)

3192mJ/sq.cm(0.5m/min)

UV-LED Irradiation period Dark period UV-LED Irradiation period w/pre-IR

Curing speed and energy under continuous/intermittent irradiations in sensitized systems

IR output: 3.2kW

Sensitized cationic initiation system with and without pre-IR irradiation

RadTech 2018 Technology Expo & Conference | Kaz Ashikaga | May 8, 201814

O

O

C

C

O

O

+

Sensitizer Photo-initiator

Initiation species

9,10-Dioctanoyloxy anthracene

I+ CH2CH(CH3)2H3C

PF6-

IMMPH (250)

0 100 200 300 400 500 600

50on/150off

40on/150off

30on/150off

ContinuouslyON

Process time(msec)

828/250/581＝100/4/1Minimum 

required energy(Maximum speed)

290mJ/sq.cm(35m/min)

595mJ/sq.cm(2m/min)

278mJ/sq.cm(4m/min)

318mJ/sq.cm(5m/min)

0 100 200 300 400 500 600

PreIR+50on/150off

PreIR+40on/150off

PreIR+30on/150off

PreIR+Continuously ON

Process time(msec)

828/250/581＝100/4/1 Minimum required energy(Maximum speed)

253mJ/sq.cm(40m/min)

238mJ/sq.cm(5m/min)

158mJ/sq.cm(7m/min)

198mJ/sq.cm(8m/min)

UV-LED Irradiation period Dark period UV-LED Irradiation period w/preIR

IR output: 6.4kW

Post IR irradiation effect for cationic curing system

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UVLED

Post-IR

0 100 200 300 400 500 600

50on/150off +PostIR

40on/150off +PostIR

30on/150off + PostIR

Continuously ON+PostIR

Process time(msec)

828/250/581＝100/4/1 Minimum required energy(Maximum speed)

50mJ/sq.cm(200m/min)

397mJ/sq.cm(3m/min)

222mJ/sq.cm(5m/min)

159mJ/sq.cm(10m/min)

Off line IR irradiation 50m/min

• Post IR irradiation is efficient to increase curing speed for cationic curing system

IR output: 6.4kW

• Intermittent irradiation can provide efficient curing in TPO initiation system by reducing termination reaction of propagation radicals by radical coupling.

• Pre-IR irradiation can remarkably accelerate curing speed for both intermittent and continuous irradiation processes in TPO initiation system.

• Intermittent irradiation can also work to reduce total energy for curing in sensitized phenyl ketone initiation systems, however, no process time advantage can be observed for intermittent irradiation process, presumably due to different initiation mechanism.

• Post-IR irradiation can efficiently work for the sensitized cationic initiation system with continues LED irradiation and total energy required for curing can be reduced with shortening process time.

Summary

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