omnicure uv curing radtech 2014
TRANSCRIPT
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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