Intro Basic Uv Curing2012 Mji

7/24/2019 Intro Basic Uv Curing2012 Mji

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Introduction to the Basics of UV/EBChemistry and Formulations

SUNY ESF

Institute for Sustainable Materials andanu ac ur ng

Dr. Mike J. Idacavage

Esstech, Inc.September 27, 2012

Agenda

Introduction to UV/EB Curing

Basic Formulation strategy

Oligomers

Monomers

Photoinitiators

Cationic Cure

Electron Beam

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Energy Curable Industrial Coatings

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Energy Curable Graphic Arts Applications

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What is Energy Curing?

Using UV energy, visible light, or high energy electronsas opposed to thermal, evaporative, or oxidative (air-dr cure to form a coatin film or ink

Types of energy used for energy curing:

Ultra Violet (UV): 200 400 nm

Visible light: typically 380 - 450 nm

Electron beam: low energy electrons

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While I will try to use the term energy curable, please note that the terms radiationcurable or UV/EB curable may be used interchangeably.

Why Use Energy Curing?

Productivity, Productivity, Productivity Seconds to cure vs. minutes or hours

Lower Overall Cost (per cured part) 100% solids, cure speed, recycling of coating, etc

Single component formulas Eliminates mixing errors found in 2 component systems

Regulatory Concerns (VOC emission) Avoid solvent use in most cases

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Sma er equipment ootprint Less floor space needed

Energy costs (esp. now with high oil prices)

Did I mention Productivity?


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Areas of Strength for EC

Scratch Resistant Coatings (plastic, paper up-grade)

Over Print Varnishes

Printing Inks (Litho, Flexo, Screen)

Wood Coatings

Electronic & Fiber Optic Coatings

Photopolymer Plates

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EC can generate a high crosslink density network that results in a coating with high gloss and

hardness, scratch and stain resistance and fast cure. EC also works best with flat substrates, which

are found in all of the above markets.

Areas for Improvement

Adhesion to some metals, esp. during post-forming

Adhesion to some plastics

Tear resistance

Low gloss in 100 % solid systems

Low film weight for 100% solids

Overall cure of 3-D parts

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EC coatings can have high shrinkage, which adversely affects adhesion to non-porous substrates.

Lack of solvent coupled with a fast cure reduces the formulators ability to meet low gloss, low film

build requirements. Additional lamps are needed to cure 3D parts since EC is a line of sight cure

method.


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RADIATION CURING

TYPES OF RADIATION USED

UV - ultraviolet photons

EB - low energy electrons

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RADIATION CURING CHEMISTRY

Free Radical

Polymerization through double bonds

(Meth)Acrylate double bonds most commonfunctionality

Cationic

Polymerization through epoxy groups

Cycloaliphatic epoxies most commonly used

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Free Radical Curing - UV Photoinitiator absorbs UV light and generates free

Free radicals react with double bonds causing chainreaction and polymerization

Cationic Curing - UV Photoinitiator absorbs UV light and generates a

ew s ac

Acid reacts with epoxy groups resulting inpolymerization

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Free Radical Curing - EB

Electrons open double bonds initiatingpo ymerization - no p otoinitiatorrequired

Cationic Curing - EB

Electrons decompose photoinitiator to

-for polymerization

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UV CURING

Acrylated Resin(s)basic coating properties

CC

UU

ono unc ona onomer s

viscosity reduction, flexibility

Multifunctional Monomer(s)

viscosity reduction, crosslinking

Additives

UVUV

LightLight

EE

DD

PP

RR

OO

DD

per ormance ine tuning

Photoinitiator Packagefree radical generation

UU

CC

TT

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EB CURING

Acrylated Resin(s)CC

UU

basic coating properties

Monofunctional Monomer(s)

viscosity reduction, flexibility

Multifunctional Monomer(s)

viscosit reduction crosslinkin

RR

EE

DD

PP

RR

OO

ElectronsElectrons

Additives

performance fine tuning

UU

CC

TT

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Formulating for properties

Some desirable properties for coatings:

Adhesion

Cure speed

SARC (scratch & abrasion resistant coatings)

Weatherability

Flexibility

Pi mented s stems

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Everything You Always Wanted to Know About UVFormulating

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Formulation of EC Products

FormulaLamp

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Application

All three aspects are interrelated

FORMULATING A UV CURABLE SYSTEM

PHOTOINITIATORSPHOTOINITIATORS

ADDITIVESADDITIVES

MONOMERSMONOMERS

OLIGOMEROLIGOMER

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ADDITIVESADDITIVES

MONOMERSMONOMERS

OLIGOMER

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OLIGOMER TYPES

(Meth)Acrylated

Epoxies

Characteristics

fast curing, hard, solvent resistant, lower cost

Aliphatic Urethanes

Aromatic Urethane

Polyesters

flexible, tough, non-yellowing, best weatheringproperties

flexible, tough, lower cost than aliphaticurethanes

low viscosity, good wetting propertiesies

Acrylics

Specialty Resins

good weathering properties, low Tg

adhesion, special applications

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Epoxy Acrylate

OLIGOMERS

bisphenol A diglycidyl ether diacrylate

CH2 CH C O CH2 CH CH2 O C

CH3

CH3

O CH2 CH CH2 O C CH C H2

OOHOHO

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Urethane Acrylate

OLIGOMERS

aliphatic urethane diacrylate

CH2 CH C O R O C NH CH2 NH C O R' O C NH CH2 NH C R O C CH CH3

O OO OOO

CH3 CH3

CH3 CH3

CH3 CH3

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ADDITIVESADDITIVES

MONOMERS

OLIGOMEROLIGOMER

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MONOMERS

Monofunctional Monomer

CCHH33 CCHH33

CCHH33

OOCC

OO

CCCCHH22

HH

IBOAisobornyl acrylate

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MONOMERS

Difunctional Monomer

O O

TRPGDAtripropylene glycol diacrylate

CH2 CH C O (C3H6O)3 C CH CH2

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MONOMERS

Trifunctional Monomer

O

CHCHCOCH

CH3 CH2 C CH2 O C CH CH2

O

O

CH2CHCOCH2

TMPTAtrimethylol propane triacrylate

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Cure

Speed

Monomer Selection

Flexibility AdhesionVisc.

ReductionResidualUncured

-

Func.

Di-

func.

Trifunc. &

Hi her

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Like all generalizations, these trends are usually, but not always, true


ADDITIVESADDITIVES


MONOMERSMONOMERS

OLIGOMEROLIGOMER

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ADDITIVES

Pigments Flatting Agents

Fillers

Defomers

Wetting Agents

Slip Aids

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ADDITIVESADDITIVES


MONOMERSMONOMERS

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Photoinitiators

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Terms/Glossary

max(pronounced lambda max)

The wavelength at which photoinitiator absorbs the most

energy; also known as peak absorbance

absorbance The amount of light a material takes in as opposed toreflecting or transmitting it

cure The conversion of unreacted material to reacted material;transformation of monomers and oligomers to a polymer

network; in practical terms, usually the point at which the wet

material reaches a mar free state (or any other property of

interest)

photons A quantum of light; a packet of light energy

polymerization The reaction by which monomers (and oligomers) areconverted to high molecular weight materials (polymers)

radical AKA free radical, molecule fragment with 1 unpaired electron.Not an ion (has no charge)

transmission The amount of light passing through a material; the ratiobetween the outgoing (I) and the incoming intensity (Io),

%T = (I/Io) x 100

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Why Are PI Necessary?

PI Characteristics Absorb UV light or electrons to form active species (radicals

or acids)

Add to monomer/oligomer to start cure process(polymerization)

Different PI absorb UV light at different wavelengths

Match PI with UV lam out ut

Only reacts with UV-Vis energy, not heat

Long pot life/shelf life

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Initiation System is irradiated, reactive species (free radicals) created

Pro a ation

UV Radical Polymerization

Oligomers and monomers add to the growing polymer chain,creating a high MW network

Termination Two radicals combine to stop the chain reaction

termination

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Initiation Process

System is irradiated and the photoinitiator absorbs some of

Initiation

the incoming energy

Photoinitiator forms one or more free radicals

A free radical then combines with an acrylate to form a newradical that is the active species for the growing polymer

UV polymerization is line-of-sight only shadowed areas very

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Propagation Process

Propagation

Free radical

on end of polymer

chain

Reacts with an

acrylate to make a

Referred to as a chain reaction

new radical

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Termination Process Two radicals (active species, growing chains, PI fragments)

Termination

If PI concentration is too high, the radicals from the PI cancontribute to a high termination rate

A high termination rate can lead to Greater levels of unreacted material

Poor physical properties (e.g. low adhesion, greater marring, poor

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Initiation

Summary

I 2 IUV Energy

I + M IM

Propagation

IM + M

IMM + M

IMM

IMMM

P~M + M~P P~M-M~P- -

IMMM + M IMMMM

P~M + I P~M-I

- -

I = Initiator M = Monomer (or any acrylate) P = Polymer chain

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Classes of Photoinitiators Photocleavage (unimolecular PI)

a-cleavage PI - Adsorbs light and fragments to form theradicals which initiate polymerization.

Photoabstraction (bimolecular PI)

Hydrogen abstraction PI - Adsorbs light and abstractshydrogen from another molecule (photoactivator) whichproduces radicals.

Amine synergist (photoactivator) - Donates a hydrogen to thep o osens zer o pro uce e ra ca s w c n a epolymerization.

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Photoinitiator, photosensitizer, and photoactivator are often used as differentwords for photoinitiators even though they are not the same

Liquids are easier to handle in a plant (but often $$)

Photoinitiator Mixtures (liquid blends)

PI blends offer advantages

Absorb over a larger range of wavelengths better chance ofavoiding interference from e.g. pigments and make use ofmore of the available UV energy

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Photoinitiator Selection

Absorption characteristics of photoinitiator

and formulated system

Pigmentation

Spectral output of UV lamps

Oxygen inhibition

Weatherability (yellowing)

Handling (liquid vs. solid)

Toxicity

Cost

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Matching PI with UV lamp

Different UV lamps emit energy in different part of the spectrum

Need to match absorbance of the PI with the output of the lampor ig est e iciency

PI / Lamp Output Match

(Additol CPK / Fusion "H" bulb)

Good absorbance (PI) + Good energy output ("H" bulb) = Good match

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200

210

220

230

240

250

260

270

280

290

300

310

320

330

340

350

360

370

380

390

400

410

420

430

440

450


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Oxygen inhibition

Oxygen can inhibit (slow down) the cure speed of coatings andinks, especially in thin layers

Solutions:

Amine synergists

Cure under an inert (N2) atmosphere

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Cationic Cure

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CATIONIC CURING MECHANISM

Initiation (Light & Heat)

O

R H+MF 6

-

O

R

H+

O

R

O

R

R

HO

+

initiation

h

photoinitiator

HO

R+

CATIONIC CURING MECHANISM

Polymerization (Chain Reaction; Heat)

polymerization

O

R

O

R

R

HO

+

O

R

R

O

R

R

O

n

+

chain reaction

mO

R

HO


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Radical vs. Cationic

Radical Cationic

wide variety of raw materials more limited raw materialsinhibited by oxygen not inhibited by oxygennot inhibited by high humidity inhibited by high humiditynot inhibited by basic materials inhibited by basic materialsfull cure in seconds full cure in hoursshrinkage - greater shrinkage - lessadhesion - less adhesion - greaterep o cure - grea er ep o cure - ess

cost - less cost - greater

UV/EB market share - 92-94% UV/EB market share - 6-8%

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UV Cationic Curing

Cycloaliphatic Epoxide(s)

basic coating properties

CU

UV

Light

Polyol(s)

crosslinking, flexibility

Epoxy/Vinyl Ether Monomer(s)

viscosity reduction

Additives

performance fine tuning

ED

PROD

oto n t ator ac agecation generation - commonly sulphonium salts

UCT

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Cycloaliphatic Epoxides

Epoxides

Major Component of the formulation

Builds properties of the film

Other components are modifiers

CH2 O C

O

O

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Electron Beam

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ELECTRON BEAM

Ionizing radiation or low energy electrons (e)

have sufficient energy to break bonds in coating, and generate free

can penetrate into and through a coating/ink, and through somesubstrates

are not affected by pigmentation or transparency of coating/ink orsubstrate

generate little to no heat

dose can be precisely controlled

enable high through put

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E BEAM PARAMETERS

Voltage = Electron Penetration

Equals Thickness Penetrated

units are e volts: MeV, keV

Amperage = Beam Current

Equals Exposure Intensity

units are amps

=

Expressed in kGy (kiloGray) or Mrad (mega rad)

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High Voltage E BEAM PENETRATION

10

12

eV

0

2

4

6

8

Voltage,

Penetration, mils

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LOW VOLTAGE E BEAM PENETRATION

300

350

V

0

50

100

150

200

250

Voltage,

0 5 10 15 20

Penetration, mils

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eAND hv PENETRATION

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LOW VOLTAGE E BEAM

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Thank You!

Dr. Mike J. Idacavage

Director of Business Development

Esstech Inc.

Email: [email protected]

Phone: 1-610-422-6589

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