Elsworth VOM UV_Presentation
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Transcript of Elsworth VOM UV_Presentation
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Breakthrough Innovations in UV/Visible
Light Curing Materials and Systems
Jeffrey Payne, Ph.D.
Chief Marketing OfficerEllsworth Adhesives
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Presentation Outline
The basics of light curing material chemistry
Advantages/disadvantages of different chemistries
UV and visible Light emission and absorption
Photoinitiators and cure
Oxygen inhibition
LED light sources for curing
Process Control
UV curing equipment
UV materials in Electronics applications
See-CureTM Technology
Ellsworth Adhesives
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Why UV/Visible Light Cure
Most common answ er is speed, but also
One-part systems no mixing, purging, waste
Solvent-free systemsIn-line inspection
Performance
Bottom line lower processing costs
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Components of Light Curing
Materials
OligomersHigh molecular weightmolecules with multiplereactive sites
MonomersMolecules that crosslink with
each other and oligomers
AdditivesThixotropes, tracer, color,conductive, etc
CatalystsPhotoinitiators and othercatalysts, especially peroxides
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UV Product Chemistries
Acrylate Urethanes:Oligomers are urethanes with acrylate functionality (and possibly isocyanatefunctionality) that crosslink with acrylate monomers. Cure with photoinitiatorand peroxide catalysts. Isocyanate functionality provides moisture cure.
Acrylate Rubbers:Oligomers are rubber based (isoprene, butyl, etc) with acrylate functionalitythat crosslink with acrylate monomers. Cure with photoinitiator and peroxidecatalysts.
Cationic Epoxy:
Oligomers have a variety of backbone structures and are epoxy functional.Crosslink with epoxy monomers. Catalyzed by cationic photoinitiators.Propagation reaction is not quenched by oxygen therefore propagationcontinues after light activation. Accelerated by heat.
Silicones:Oligomers based on silicones. Acrylate UV cure. Secondary RTV moisture
cure, methoxy.
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Acrylate Urethanes
Been around since early 1980s
Terrific variety of Oligomers and Monomers
Utilize photoinitiators over wide wavelength rage
Secondary cure with heat when peroxides used as catalyst
Secondary cure with humidity when some isocyanate left
unreacted with acrylate groups during oligomer synthesis
Suppliers of Conformal Coatings with UV primary and
humidity secondary cure:
Dymax Emerson & Cuming
Henkel Humiseal
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Acrylate Rubbers
New technologies made possible by innovations in oligomer
chemistry
Smaller but growing number of products
Known for flexibility, softness, chemical/heat resistance
Utilize same photoinitiators as acrylate urethanes
Can react with peroxide
Do not cure with humidity
Many suppliers including:
Dymax Henkel Permabond Resin Design
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Cationic Epoxies
Newer class, last 15 yearsPhotoinitiator splits to form an acid, not radical
Cure not inhibited by O2Cure rate increased with heat
Reaction is somewhat slower
Reaction continues after light exposure is terminated, butdoes not reach into shadows
Two-part systems available activated with light
Many of the properties of epoxies relative to acrylatechemistries apply:
Higher heat resistance and Tg, generally
Higher solvent resistance
Lower shrinkage
More rigid, generally, though there are important
exceptions
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UV Silicones
UV primary cure acrylate monomers andsilicone oligomers with reactive acrylatefunctionality
Moisture secondary cure methoxy terminatedsilicones
Provide a balanced set of properties typical ofacrylic and silicone systems.
Nuva-Sil products from Henkel/Loctite are theprimary example
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200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700
Wavelength, nm
UVC UVB UVA
Curing Range of UV Assembly Materials
UV Products: Cure with light from 320-400 nm
UV/Visible Products: Cure with light from 320-460 nm
UV and Visible Electromagnetic Spectrum
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Images courtesy of Heraeus
Basics of UV LampsMercury and Metal Halide Mercury Lamps
Mercury vapor provides conduction between
anode and cathode.
Emission spectrum determined by chemical
gases.
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Absorption Spectra of Common
Photoinitiators
All photoinitiators absorb at short wavelengths.
Formulators try to find absorption at higher wavelengths to reduceoligomer/monomer/substrate interference increase depth and speed of cure
Courtesy of Ciba
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Quantum Mechanics Revisited
Energy levels in a photoinitiator are discrete, not continuous
Overlap between an emission spectrum and an absorptionspectrum is a precursor of a good match. Most of the PIabsorption bands do not relate to PI splitting. Quantitativeresults can only be achieved through system experimentation
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Matching Photoinitiators to the Job
All organic molecules absorb UV light Most turn the light to heat ( think sun on black pavement)
Some split or react photoinitiators to form energetic reagents
Since photoinitiators compete with oligomers, monomers, andother formulation ingredients, formulators choose photoinitiatorsthat minimize interference.
Long wavelength photoinitiators that absorb UVA and visible lightare preferred for
Adhesives
Sealants
Conformal Coatings
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UVB/UVC Absorbed Rapidly byOligomers/Monomers Surface cure only. Inks, etc.
UVA penetrates deeperinto bulk formulation.Deeper cure. Oldertechnology.
Visible light penetratesdeeper. Not blocked byUV blocking materials orplastics. Newerphotoinitiators reactiveto visible light.
BulkUVMater
ial
Photoinitiators Chosen to Take
Advantage of Available CuringLight
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The Problem Of Oxygen Inhibition
Free radicals are scavenged by O2
Acrylate system cures are therefore inhibited by O2 (notcationic cures)
Oxygen inhibition is most important at the material surface
Oxygen inhibition is overcome by:
More curing power overwhelm O2 by creating moreradicals
Shorter wavelength concentrate power at the surface
where interference is minimum and PI absorption is
maximum
Fast reacting formulations
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One More Thing About O2Inhibition
The peroxide secondary cure used in acrylate urethanes andrubbers are radical cure mechanisms too
Therefore, the heat cure polymerization of these systems isseverely inhibited by O2
Heat cure of acrylate urethanes and rubbers will not yieldtack-free surfaces the reaction is too slow relative to O2
scavenging
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Todays Formulators Utilize
Photoinitiator Combinations thatMatch Application and CuringSystem
To get surface cure (acrylate systems), use a PI reactive in themiddle of UVA range. Even some UVB.
To get depth of cure (all systems) and cure through UV blockedsubstrates, use a PI reactive in the visible range (normally 400-460 nm)
Combination utilizes a large portion of the emission spect ra ofUV D type bulbs from 340 nm (high end of UVB) to 460 nm
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Typical UV LED Emission
Spectra
Emission spectra of two Ocean Optics LED s in the UVA range.
LEDs mounted in arrays w/o reflectors
Point sources spread over a large areamaking focus less efficient
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Advantages and Disadvantages
of LED Sources
Disadvantages:
Very narrow emission band. PI
capabilities not utilized
Relatively low power even at peak
wavelengthWeak power against O2 inhibition (not a
problem for cationic epoxies)
Focusing
Advantages:Instant on/off shutter not required
Very long life
Essentially no intensity degradation
Low heat to lumen ratio. No wasted light
LED Source
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Bulb Degradation
Anode/cathode/mercury vaporbulbs degrade with use due todegradation of the anode andcathode tips. Bulb intensitydeclines with use.
Three ways to deal with bulb degradat ion
1. Monitor degradation with an external radiometer and adjustprocess and change bulb per assembly requirements.
2. Use a UV light system that does not degrade with use(LED.Microwave)
3. Use a system that automatically adjusts to bulb intensitychanges, photofeedback control.
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External Radiometers
Dymax Accucal 50 canmeasure intensity and energyfor flood and spot lamps
Establishing a consistent assembly processrequires
1. Determining the minimum intensity andcure time (energy) for a process.
2. Maintaining the intensity and time(energy) for the process as bulbintensity changes with time (for arcbulbs)
Energy ordose is the product of intensityand time. Intensity measured inmW/cm2. Energy measure in mJ.
Normally process set around minimumintensity required and radiometer usedto indicate bulb change as bulbdegrades.
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Process Control
It is very difficult to over cure UV products
External radiometer process control requires user toestablish a minimum acceptable intensity and changebulb once intensity falls to minimum. Initial start pointafter bulb change is higher than minimum. Excessintensity above minimum is unnecessary but notharmful.
Internal radiometer control maintains constantintensity as bulb degrades. Process maintained atintensity minimum. Feedback mechanismcompensates for diminishing bulb output.
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LED and Microwave Sources
Have Essentially No IntensityDegradation
Dymax BlueWaveTM LED Spot System
UVPS LED Flood System for Conveyor
Fusion Microwave on Dymax Conveyor
UV LED sources and Microwave sources last for
up to 50,000 hours with essentially no reduction inlight intensity
ON/Off cycling does not lead to intensitydegradation
Radiometer useful in establishing process, but notcritical in maintaining process
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Photo Feedback Eliminates Need
for Radiometer to MaintainProcess
Lesco Spot Lamps Utilize Photo Feedback
An internal radiometer monitorslight intensity and automaticallymodifies either power to bulb orlightpath to lightguide tocompensate for bulb degradat ion.
Requires initial intensity belowmaximum after new bulbinstallation
Lesco increases power to lamp tocompensate for diminishing bulbintensity
Exfo opens iris between bulb andlightguide as bulb output
decreases
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Spot Systems
(some examples)
Dymax BlueWaveTM
200 or 50 Watt
Metal Halide or LEDManual Intensity Control
Loctite Zeta 7740
100 Watt
Metal HalideOptional Intensity Alarm
Lesco (AUV) Super Spot
100 Watt
Metal HalideAutomatic IntensityControl
Mercury vapor bulb mounted in parabolicreflector
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Flood Systems
(some examples)
Lesco (AUV) Cure Max
400 WattMetal Halide
Many different size/shutteroptions
Loctite Zeta 7411-S
400 WattMetal Halide
Dymax 5000/2000 EC
400 WattMetal Halide
Many different size/shutteroptions
400 Watt Mercury Vapor MetalHalide Bulb
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Conveyorized Systems
(some examples)
Top Dymax MetalHalide
Bottom Dymax
With FusionMicrowave
Top Loctite Metal Halide
Bottom Loctite
With Fusion Microwave
Top UVPS LEDArray, mountable
Bottom UVPS LED
Array, Mountable
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Light Curing Products in
Electronics Applications
Conformal CoatingsUsed in a great number of end uses, especially Defense,
Automotive, Appliance
IPC, MIL, UL approved formulations
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Light Curing Products in
Electronics Applications
Encapsulants
Particularly good for flex
Excellent forcold soldering (encapsulating
conductive epoxy bonded components to
flex) for hold during epoxy cure
Potting Two-part UV Epoxy from Resin
Design
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Light Curing Products in
Electronics Applications
Peelable Masks
Tacking AdhesivesSealing, Especially for LCDs
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Dymax See-CureTM
Technology
Idea is that adhesive changes color as the adhesive is cured
Several combinat ions including clear to colored and colored
to clear
Technology is useful for seeing where the productis dispensed and whether the product has beenexposed to UV light.
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A Word About Ellsworth
AdhesivesWorlds largest distributor of UV/Visible Light Curing
products for product assembly
Specialists in the Electronics field, 40% of business
Over 100 Engineering Sales Representatives worldwide
Approximately 40 stocking location worldwide
Represent major lines, including:
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Thank You