Elsworth VOM UV_Presentation

8/7/2019 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


Dymax 5000/2000 EC


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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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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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

Elsworth VOM UV_Presentation

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