Excelitas Technologies

The Technical Challenges of Transitioning your UV Curing Process from Lamp to LED

Mike Kay

Director of Product Management, OmniCure

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

Our Expertise

RADIOMETRY

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

Typical Applications: Adhesive Curing

• Medical Devices: – Balloon catheters

– Ablation catheters

– Prefilled syringes

– Anesthesia masks

– Endoscopes

– Tube sets

– Filters

– Blood oxygenators

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

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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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)

LED Longer Lifetime = Lower Cost of Operation

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• LED typical lifetime = 20,000+ hours

• 10% degradation in first 500 hours

Test Data for LED Lifetimes

Estimate 75% of Original output at 29,000 hours with 25°C Ambient temp.

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

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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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)

Mic

roh

ard

ne

ss

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

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

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

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

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

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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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

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

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

Initial Material Testing: Lamp vs LED

• 24 Direct 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?

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 650Wavelength (nm)

Typical 200W Lamp Output No Filter

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.

Thank You

Questions?

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