Light curing inks, coatings and adhesives employ a photoinitiator to trigger the hardening of the material

2. Excelitas Technologies
The Technical Challenges of Transitioning
your UV Curing Process from Lamp to LED
Mike Kay
Director of Product Management, OmniCure

3. Who We Are
• Lumen Dynamics was acquired by Excelitas
Technologies Company in November 2013
• Excelitas has over 5,000 employees worldwide
• Global network of design and manufacturing locations
in the Americas, Europe and Asia
• Design and creation of innovative UV curing solutions
since 1984
• Over 30,000 UV curing systems currently being used in
more than 50 countries
• Lamp and LED UV systems

4. Our Expertise
RADIOMETRY

5. UV Curing Technology
• Light curing inks, coatings and adhesives
employ a photoinitiator to trigger the
hardening of the material
• When sufficient light of the correct wavelength
range is absorbed by the photoinitiator, it will
begin the curing process
• If the formulation receives enough light energy
to complete the reaction, the cross linking
process will transform the liquid into a solid
• The physical properties of the finished product
are critical to the manufacturing process

6. Typical Applications: Adhesive Curing
• Medical Devices:
– Balloon catheters
– Ablation catheters
– Prefilled syringes
– Anesthesia masks
– Endoscopes
– Tube sets
– Filters
– Blood oxygenators

7. Benefits of UV Curing
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 Instant Cure: Product immediately ready for next process stage
 Reduced Cycle Times: Improves production speed & ease of
automation
 Control of Cure: Cure-on-demand, or vary degree-of-cure
 Energy Savings: 1-4% of energy vs. water-borne/solvent adhesives
 Derivative Savings: Reduced solvent use, less floor space etc., can
save up to 30% vs. traditional assembly
 Ease of Coating: Single-component systems, lower viscosities, and
wide range of cured physical characteristics
 Environmental/Safety: No VOC emissions, reduced regulatory
requirements, and low flammability

8. Benefits of LED Curing Systems
• Low Temperature Curing
‒ Higher yields
• Lower Running Costs
‒ Lower power consumption
‒ Long lifetime LED heads
• Easy Integration
‒ PLC control
‒ No venting required
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9. Environmental – LED Leads the Way
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• UV Curing is considered a green
technology
‒ Lower solvent, VOC content than other
adhesive technologies
• LEDs are mercury free
• LEDs do not generate ozone
• LED systems require up to 80% less input
power
• No consumable items (eg. lamps, light
guides)

10. LED Longer Lifetime = Lower Cost of Operation
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• LED typical lifetime = 20,000+ hours
• 10% degradation in first 500 hours

11. Test Data for LED Lifetimes
Estimate 75% of Original output at 29,000 hours with 25°C Ambient temp.

12. Radiometry
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• LED degradation slower than lamps, but
still enough to require a radiometer
‒ Requirement for any repeatable assembly
process
• Technology for LED radiometry still being
developed; challenges include:
‒ Narrowband spectral distribution
‒ Narrow beam patterns
• New systems being released with specific
technology to overcome challenges
‒ Radiometry designed for lamp-based
systems will not be accurate

13. Light Cure Factors
• Light conditions which can affect final cured
properties are:
‒ Irradiance level
‒ Exposure duration
‒ Spectral content
‒ Heat
• A light-curing adhesive exposed to different
curing conditions, will exhibit different
physical properties:
‒ Flexibility
‒ Moisture resistance
‒ Bond strength
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14. UV Curing Power
• Irradiance: Radiant power arriving at a
surface, per unit area (W/cm2)
• Radiant Power: Rate of Energy
transfer, expressed in Joules/sec
• Sufficient energy must be received to
convert the photoinitiator and begin
the curing reaction
• However, excess irradiance can have a
negative effect on the cured properties
‒ YES, it is possible to cure a UV adhesive
too quickly
• LED systems must allow for adjustment
of irradiance
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Microhardness vs Irradiance (at constant Dose)
30.0
35.0
40.0
45.0
50.0
55.0
60.0
65.0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00
Irradiance (W/cm^2)
Microhardness

15. Irradiance vs Working Distance
• Irradiance levels drop significantly
over distance
• Irradiance measurements at 0mm
working distance do not represent
energy at cure site
• Optics can be used to focus the light to
specific working distances
• Need to know the irradiance level at
your working distance
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365nm 395nm
1mm 4.5W/cm2 9.0W/cm2
10mm 3.3W/cm2 6.5W/cm2
30mm 1.5W/cm2 3.0W/cm2

16. Optics Allow for Increased Working Distances
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Irradiance @ 1mm Irradiance @ 20mm
LED System with lens 9.0W/cm2 4.5W/cm2
LED System no lens 8.0W/cm2 1.5W/cm2
With lens
No lens

17. Spectral Content
UVV UVA UVB UVC
Lamp* 40% 45% 12% 3%
365nm LED 1% 99% 0% 0%
400nm LED 97% 3% 0% 0%
* Results will vary by lamp

18. Spectral Content: Curing Requirements
• Effective Irradiance: Radiant power, within a
specified wavelength range
• Sufficient light of the correct wavelength
range must be received by the photoinitiator
to begin the curing reaction
• Critical to match the wavelength of LED to
the absorption spectra of photoinitiator
‒ If they do not match, the material will not
cure, regardless of irradiance level
‒ 365nm, 385nm, 395nm and 405nm
wavelengths available to match the
photoinitiator requirements
Photoinitiators absorption curves
Plots courtesy of CIBA Specialty Chemicals

19. Spectral Content: Lower Heat with LED
• Light is absorbed by the adhesive
components and converted into heat
• Light absorbed by the materials being
bonded generates heat
• Narrow spectrum of LED ensures reduced
heat in curing
• Reduced heating in the curing process can
help to increase product yields
Sample temperature measurements
for lens bonding application

20. Which LED Wavelength to Choose?
• Many formulations will specify 365nm
‒ Designed to match 365nm peak of Hg lamps
• Many free radical formulations will cure
with wavelengths up to 420nm
• Many cationic photoinitiators have
absorption spectra that cuts off at 380nm
• Curing with 400nm LED generally provides a
better through cure
• Curing with 365nm LED generally provides a
better surface cure
• 400nm LED systems will generally have
significantly higher power than 365nm
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21. Substrate Must be Considered
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• Adhesive specifies 365nm
• Transmission of light through the
substrate:
‒ 50% at 365nm
‒ 80% at 395nm
• 60% more 395nm light gets to
the adhesive
Results
• 395nm LED cures faster and with
less heat than 365nm LED
Absorption Curve of Substrate

22. Adhesive Compatibility
• Many adhesives contain multiple
photoinitiators, with varied
absorption peaks
– Take advantage of broad
spectrum of Hg lamps
• What happens when an adhesive
designed for a broad spectrum is
cured with a narrow band of
light?
Adhesive absorption spectra

23. Initial Material Testing: Lamp vs LED
Microhardness Test Results
Indirect testing (microhardness)
• Indicates adhesive is likely cured equally well
• Results would indicate that adhesive sample is
cured equally with lamp and LED
sample weight
(g) light source power
distance
(mm)
exposure
time (s)
microhardness
reading (avg)
0.0286 Lamp 5W/cm2 10 5 59.6
0.0241 LED 5W/cm2 10 5 62.3

24. Initial Material Testing: Lamp vs LED
• 24Direct analytical testing (DSC)
• Shows amount of uncured
material
• Significantly more uncured
material with LED source
Uncured
material
Is curing with LED really equal to lamp for this adhesive?

25. Surface Finish
• Free radical adhesives are susceptible to
curing with a tacky surface when exposed
to air
‒ Oxygen inhibition
• Formulations available to minimize
problem
• Ways to minimize in your process
‒ N2 purge
‒ Exposure to short wavelength UV
(UVC: 250-285nm, UVB:285-315nm)
‒ High peak irradiance
‒ Heat
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0
100
200
300
400
500
600
250 300 350 400 450 500 550 600 650
Wavelength (nm)
Typical 200W Lamp Output No Filter

26. Summary
• Benefits of LED Systems include:
‒ Lower heat
‒ Lower cost of operation
‒ Environmental
• Potential Challenges:
‒ Radiometry
‒ Adhesive compatibility
‒ Surface cure
Changing light sources is changing your process.
Testing is the only way to confirm compatibility.

27. Thank You
Questions?
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