Expanded Opportunities:

UV Inks on Coldset Web Presses A PRINTER’S HANDBOOK

Table of Contents

Introduction .............................................................................................................. 3

Key Benefits of Energy Curable Inks ..................................................................... 4

The Basics ................................................................................................................ 5How Does UV Work? ........................................................................................... 5Changes Recommended for Conversion to UV Inks ............................................. 5Switching Between Conventional and UV Inks ...................................................... 5Drying vs. Curing .................................................................................................. 6Rudimentary Chemistry ........................................................................................ 7Applications ......................................................................................................... 7Equipment............................................................................................................ 9

Environmental ........................................................................................................ 11Energy and Emissions ....................................................................................... 11De-Inking............................................................................................................ 11

Health and Safety ................................................................................................... 12Precautionary Steps ........................................................................................... 12First Aid ............................................................................................................. 13

Ink Handling ........................................................................................................... 14

Glossary .................................................................................................................. 15

The printing industry changes dramatically onan almost daily basis. One of the most rapidlyadvancing technologies is Energy Curing, ageneral term which refers to inks and coatingsthat are cured, or hardened, by exposure toradiant energy. That energy can be in the formof Ultraviolet Light (UV).

This booklet was developed to help printersbetter understand the growing applications forUV inks, specifically on coldset web presses.

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With a relatively small capital investment, acoldset web printer can increase his or heropportunities from printing only on newsprint to

having the capacity to print on a wide variety ofstocks, ranging from newsprint to supercal andeven to coated stocks.

Introduction

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Key Benefits of Energy Curable Inks for Coldset Web Presses

1. Capable of being printed on a widerrange of substrates: coated, supercal,and newsprint

2. Instantaneous drying: inks are touch dry atthe end of the press

3. Improved color reproduction: brighter,sharper images with no dry-back

4. Reduced start-up waste

5. Improved rub and mark resistance

6. Elimination of build-up on the pipe rollerand former board

7. No page-to-page set-off or marking instacks

8. Compliant with clean air regulations;VOC-free

9. Lower energy costs than those associ-ated with heatset printing

10. Improved mileage when compared tocoldset ink

11. Low odor

12. Higher gloss than coldset inks

The Basics

How Does UV Work?

UV inks contain photoinitiators that, whenexposed to ultraviolet light (200-400 nano-meters), initiate a reaction that transformsliquid and high viscosity oligomers (monomersand polymers) into a solid film. A chemicalprocess, curing, occurs crosslinking the indi-vidual oligomers into a continuous solid film.UV lamps must be installed at the end of thepress before the folder (wet trapping).

Please consult with a lamp manufacture as tothe lamp requirements for your particular print-ing situation (press, type of stocks, operatingspeeds).

Changes Recommended forConversion to UV Inks

Compatibility is a critical issue for the conver-sion from printing conventional oil inks to UVinks. In particular, the hydrocarbon solventspresent in press washes and inks are verydetrimental to the performance of UV inks.Residual hydrocarbon solvent will inhibit curing.Factors that will need to be considered, inaddition to the installation of UV lamps, are:

• Rollers: If only UV inks will be used, thepreferred roller compounds are Buna-N/Buna Nitrile or EPDM. If both conventionaland UV inks will be used, it is advisable toconsult your roller supplier, as some con-ventional inks are known to shrink nitrilecompounds. Conventional hydrocarbonsolvents, press washes, and inks will causeswelling of EPDM rollers and will inhibitcuring of the ink film. The roller manufacturerwill probably recommend a softer roller(durometer less than 30) for UV inks.

• Blankets: If only UV inks will be used, thepreferred composition is EPDM or Buna-N/Buna Nitrile, but if both conventional and UVinks will be used, EPDM will not be suitable.

• Wash-up Solutions: UV inks will requirewash-up solutions formulated specifically forUV inks. The selection of a wash-up solutionis more critical for the UV process than forconventional inks. Swelling and degradationmay occur if the improper roller or blanketwash is used. Please consult with yourblanket and roller manufacturers as to whichwash-up solutions they have evaluated andapproved.

• Fountain Solutions: The recommendedtype of fountain solution is a mild acidsolution. Most neutral solutions are notaggressive enough to remove UV ink fromthe non-image area of the plate.

Switching Between Conventional and UVInks

If both conventional and UV inks will be used onthe same press, it will be necessary to thor-oughly clean between inks. If the cleaningbetween conventional ink use and UV inks isnot thorough, the residual hydrocarbon solventfrom the press wash and within the ink willinhibit curing of the UV film. The monomers inthe UV ink will have less of an effect on theprintability of conventional inks, however, it isstill important to thoroughly clean the pressbetween UV and conventional ink use.

Conventional to UV Inks1. Remove ink from fountain and thoroughly

clean with conventional press wash.2. Thoroughly clean rollers and blankets with

conventional roller and blanket wash.

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3. Clean blankets with a UV wash.4. With the impression cylinder off, apply a

roller compound to the rollers and allow thepress to run for 15-20 minutes.

5. Clean rollers with UV wash and put ink intothe fountain.

6. Drain and replace the fountain solution.

When properly conditioned and inked, therollers should have a wet appearance. If therollers appear dry, clean off with wash andrepeat steps 4-6. Remember, residual hydro-

“Drying” vs. “Curing”

In simplest terms, drying of an ink film occurswith conventional inks when the ink vehicle(solvent/oil) evaporates or is absorbed, leavingbehind the solids (pigments, resins, waxes,driers, etc.) to form a film on the substratesurface.

In energy curing, on the other hand, all of thecomponents in the ink or coating remain on thesurface of the substrate but are chemically

transformed into a hard film through exposureto ultraviolet lights (UV).

The difference lies in the chemistry of thematerials contained within the formulation ofthe inks and in the pressroom equipmentneeded to “energize” the curing process.

Below is a graphic illustration of the relation-ships of the various ingredients:

carbon solvents from the press wash and inkwill inhibit curing of UV inks.

UV to Conventional Inks1. Remove ink from fountain and thoroughly

clean with a UV wash. Wipe the fountainclean with a damp rag soaked with aconventional wash-up solution (use nitrilegloves).

2. Thoroughly clean rollers and blankets withUV roller and blanket wash.

3. Rinse with clean water.

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posed to ultraviolet light.The excitedphotoinitiator passes that energy to theother components of the formulation. At thatpoint, any component which becomesexcited has the ability to attract other com-ponents to itself and transfer energy to thenewly attracted component.

• Additives: Additives include waxes,wetting agents, and rheology modifiers(viscosity). They provide the added custom-izing touches to the ink.

• Pigments: Pigment particle size andconcentration can affect the curing rate ofa UV ink. Pigments are therefore selectednot only for color but for their receptivity toUV light. In addition, wetability or oil dilutionratio must be considered. Among processcolors, yellow and magenta are the easiestto cure, followed by cyan and black. Be-cause black absorbs the wave lengths ofUV light, more energy is required to obtaina satisfactory cure.

PolymerizationAny component that is excited or energized iscalled a "free radical." Free radicals have theenergy to keep the curing or “polymerization”chain reaction going. Each chemical chaincontinues growing until one of two thingshappen:

• The excited chains use up all of theavailable components, or

• Some foreign substance, such as oxygen,"quenches" or halts the reaction.

The materials used in energy curable inkformulations are considerably more "userfriendly" than ever before. Advancements inraw materials will continue to make energycurable inks more common in the years ahead.

The major components of UV inks are:

• Reactive diluents (monomers)• Fluid resins (oligomers)• Photoinitiators• Additives• Pigments

The function of each of these chemicals is asfollows:

• Reactive Diluent (monomer): A reactivediluent monomer is a low molecular weightchemical which is similar to a solvent in itsability to thin down the ink. Monomersdetermine the surface characteristics ofthe ink – such things as gloss, hardness,and flexibility. Monomers with high draizevalues are also the chemicals which giveuncured UV inks their most hazardouscharacteristics.

• Fluid Resin (oligomer): The resin utilizedin energy curable inks is actually called an"oligomer." As in conventional inks, theresin is the chemical backbone of the ink.Among others, it provides the body, pig-ment wetting ability, and binding propertiesof the ink.

• Photoinitiators: In UV inks, thephotoinitiator is the name given to thephoto-chemical which becomes "excited"and begins the curing reaction when ex-

Rudimentary Ink Chemistry

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Polymerization Illustration

Equipment

The components of a UV curing unit are thelamp system, shielding, and ventilation.

UV Lamp SystemThe UV Lamp system consists of a quartz tube(approximately 1” diameter) typically filled witha small amount of liquid mercury and an inertgas, generally argon. When the system isturned on, the mercury is converted into avapor, emitting UV light in the 200-400 nano-meter range to cure the UV ink film. The lifeexpectancy of a typical lamp is approximately1000 operating hours. Life expectancy issomewhat detemined by the number of times itis switched on and off. Depending on thesystem installed, the lamp system will generatefrom 100 to1000 watts/square inch. The watt-age should increase automatically as the pressspeed is increased.

UV Lamp HousingThe lamp housing, also called the irradiator, isdesigned to focus the energy of the lamp ontothe substrate more effectively. The lamp is wellshielded with shutters that open automatically

Offset Sheetfed and Web printing are by farthe most widely used applications for energycurable inks. The high viscosity paste inksused for this type of printing are ideally suitedfor energy curable printing. Offset applicationscan be run both wet and dry trap depending onthe lamp configuration. Dry trap has a curingstation after every printing unit, while wet traphas a curing unit only at the end of the press.(See EQUIPMENT.)

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Over the past 15 years, improved print qualities,together with growing economic and environ-mental advantages, have created increasedinterest in energy curable inks and coatings.Today, UV curing is used in nearly every print-ing process from letterpress to flexography; onnearly every substrate from paper and paper-board to foil and film; and for both sheetfed andweb applications.

during press operation. If the web is not run-ning, the lamps are shuttered and “idle” atapproximately 30% power so that when theweb is restarted, the shutters will open and thelamps will be powered. UV lamps generate alot of heat with operating temperatures reach-ing 1100oF to 1400oF, therefore they have tobe cooled. Options include air-cooled or water-cooled systems. Lamp manufacturers gener-ally use air-cooled systems for web pressconfiguratons.

The lamp system must be direct-exhaustedto remove excess heat and the ozone gas thatis generated.

Typically, one lamp unit is installed at the endof the fourth unit. The lamp system consists oftwo lamps for the top of the web and two for thebottom, although this may vary depending onthe output of the lamps and the lamp supplier.

This is a very general description of a UV unit.Please consult the various lamp suppliers formore detailed information.

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Pressroom ComparisonConventional Oil Inks vs. UV Inks

Press washes can have a major effect on therollers’ useful life, shrinkage/swelling, andhardness. Use only washes that have beenevaluated for shrink/swell properties.

Press rollers used for conventional oil-basedinks typically are rubber compounds. If bothconventional and UV inks are to be used, itwill be necessary to consult the roller manu-facturer for specific recommendations (somemay recommend a special compound, whileothers may recommend a Buna Nitrile com-position). If the manufacturer recommends aspecial roller composition, then a conven-tional press wash should be used with the UVink. After wash-up, ensure the rollers are dry.Please consult with your press wash manu-facturer for their recommendation on whichconventional press wash to use with UV inks.

While the typical roller composition of all UVpresses are EPDM or Buna-N/Buna Nitrile,some conventional inks will shrink nitrile, thusthe press roller manufacturers should beconsulted for their recommendations. Most

UV-only printers use EPDM rollers. Thesecannot be used with conventional oil-basedinks, as they contain hydrocarbon solventswhich will cause swelling. The use of UV presswash is strongly recommended with EPDMrollers.

Blankets for conventional oil based inks aregenerally composed of three-ply rubber com-pounds. If your blanket manufacturer recom-mends rubber blankets for use with UV inks,then a conventional press wash should beused. This is not the ideal situation as it will bemore difficult to remove the UV ink. (UV blan-ket wash may swell conventional blankets.) IfBuna-N/Buna Nitrile is used with both inktypes, it is recommended that a UV wash beused. If only UV inks are to be run on thepress, then EPDM blankets and UV wash arerecommended.

UV inks perform best with mild acid fountainsolutions. Use of neutral fountain solutionswith UV inks results in slower clean-up andincreased dot gain (TVI).

Use of after burners (exhaust gas incineration)and solvent reclamation can limit emissions.However, these options have a high operatingcost and generate additional material that willneed disposal.

Energy curable inks, on the other hand, passthrough a curing unit that uses high energyelectrical power.

Furthermore, the energy curable materials are,for all practical purposes, emission-free.Although ASTM (Method 24) testing shows thematerials to contain 7-10% VOC, because thematerials polymerize rather than evaporate,these VOCs are not emitted into the air.

Recycling is an important consideration intoday’s graphic arts industry. Fortunately,newer flotation de-inking technology has

proven to be highly effective in recycling maga-zines and paperboard packaging that havebeen printed with UV curable materials.

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Environmental

Energy and EmissionsPrinting under today’s environmentalregulations has increased many printers’awareness of concerns such as energy con-sumption and plant emissions.

Conventional ink technologies such asflexography, gravure, and offset heatset rely onexposure to heated air movement as a primaryway to dry the ink film. This heated air is gener-ally provided from an oven that is fired bynatural gas. As a rule, the ovens used areinefficient and can be costly to operate not onlyin terms of fuel but in general maintenance. Theexhaust produced from ovens is laden withevaporated solvents or diluents from inks andcoatings. These exhaust materials are madeup of Volatile Organic Compounds (VOCs).VOCs are materials that contribute to airpollution which might accumulate in the loweratmosphere.

De-inking

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Health and Safety

Anyone who works in graphic arts willeventually come in contact with ink. Bothenergy curable and conventional inks arepotential skin sensitizers, which means aperson can become allergic to certain compo-nents of the inks over a period of time. Mostpeople never become sensitized; however,because energy curable inks act as a penetrat-ing liquid when spilled on skin or clothing, moreattention must be paid to ink handling proce-dures and personal hygiene than with conven-tional inks.

Personnel Affected• Ink Technicians• Press Operators and Helpers

- When mixing inks- When thinning inks- When pouring inks into fountains- When cleaning the press

• Janitor- When handling contaminated rags- When cleaning up around presses

Precautionary Steps

The following precautionary steps should befollowed by all personnel who come in contactwith inks or solvents to reduce the possibilityof becoming ‘sensitized.’

• Personal Hygiene: Use soap and waterfor cleaning hands. A UV hand cleanercan also be used for this job. Do not,however, use a conventional waterlesshand cleaner. The petroleum-basedsolvents not only dry the skin but alsoencourage skin absorption of these indus-trial chemicals.

Never eat when handling any type of inkor coating. Always wash hands beforegoing on break or to lunch!

• Clothing: Always wear nitrile gloves,aprons, and eye protection when workingwith energy curable inks. Sinceuncured ink never dries, cloth gloves oraprons are not suitable.

NEVER WEAR CONTACT LENSESWHEN WORKING AROUND ANY INKOR SOLVENT.

• Contaminated Clothing: Contaminatedclothing should be removed and washedwith lots of soap and water. Sinceenergy curable inks do not dry, clothingcontaminated with these inks should bewashed separately from other clothing.

• Shoes: Discard shoes contaminated withUV ink. Shoe covers are highly recom-mended since they are far cheaper tothrow away than shoes.

• Housekeeping: Practice good house-keeping. All ink spills, leaks, and contami-nations should be cleaned immediately withsoap and water. Conventional inks may becleaned with solvent. Wear rubber gloves.

• UV Lamps: Superficial eye damage andburning of the skin can occur with evenbrief exposure to UV light. Seriousinjuries can result from prolongedexposure, especially if unshielded.

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UV lamps operate at very high tempera-tures. Never touch a lamp which has beenin operation. Let the lamp cool beforeattempting any maintenance, and then useextreme care in handling the bulbs. Mostbulbs contain a small amount of metallicmercury which is toxic when ingested,handled, or breathed. Therefore, if bulbsare broken, care should be taken to cleanup the spill immediately.

• Ozone: Ozone gas is produced by mostUV lamps. As the lamp warms up, itbriefly passes through a section of the lightspectrum which excites oxygen moleculesenough to create ozone. Once a UV lamphas completely warmed up, only veryminute amounts of ozone are present.

Ozone has a very distinctive odor, smellingsomewhat like fresh air. Initial exposure toexcessive amounts of ozone will result indryness of the throat. Continued

exposure may cause a stronger sorethroat, but more often will result in aheadache and eventually nausea. Unlikecarbon monoxide, which actually dis-places oxygen in the blood, ozonepoisoning is a more temporary situation.However, upon continued exposure, itcan create a health problem due tosevere irritation.

• Ventilation: All UV processors should bevented to the outside. Proper ventilationserves two useful purposes:

• Small amounts of ozone emitted bythe curing unit(s) are immediatelypassed outside of the building wherethey are harmlessly dispersed.

• The venting also serves to removeexcessive heat buildup in the lampand printing area.

First Aid

• Eyes: Flush with plenty of water for atleast 15 minutes. Get medical help!Advise doctor that material contains"reactive monomers" (acrylates).

• Skin: Wash well with bar soap orpowdered soap. Do not use conventionalwaterless hand cleaner or organicsolvents.

• Ink Inhalation: Although unlikely, ifinhalation does occur, move to fresh air.Although UV inks are not volatile, if heat-ing or misting occurs, a sensitive indi-

vidual could experience an asthmatic orallergic reaction. Treat accordingly.

• Ozone Inhalation: Remove the affectedperson from the source. If he or she isnauseous, have paramedic administeroxygen.

These guidelines have been developed withthe assistance of raw material suppliers.Personal safety dictates that all affected em-ployees strictly follow safety guidelines. Foradditional information, refer to theappropriate MSD Sheet.

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table. Some components of UV ink will decom-pose slowly and will, therefore, remain active inthe environment. Inks can be disposed of in twoways:• Allow the ink to cure before discarding;• Have the ink disposed of by a chemical

incineration plant or approved chemicallandfill.

FreezingAlthough UV inks can be frozen, freezing shouldbe avoided whenever possible. If an ink is frozen,DO NOT thaw it with an immersible heater or abelt or band heater. Uneven heating of the ink willcause rapid self-polymerization.

The only way to thaw UV ink is slowly! Eithercompletely immerse the ink container in a warmwater bath (under 95°F) for not less than 24hours or let it sit at room temperature until the inkis completely thawed.

Shelf LifeMinimum UV ink shelf life in a closed container isup to 6 months, however, it is quite common forinks to remain suitable for printing one year aftermanufacture if stored correctly.

Over a period of time, UV ink will slowly reactwith itself. When this reaction first starts, a gel willbegin forming in the bottom of the container.

The only way to extend the shelf life of an ink is tostore it in a cool area in a non-metallic containerand keep a good blanket of air in the storagecontainer. Oxygen helps slow the self-curingreaction.

Ink Handling

Conditions to AvoidSome of the chemicals which make up UVinks are reactive and somewhat unstable. Inorder to make sure energy curable inks workthe way they are supposed to, there are twocategories of conditions and chemicals thatshould be avoided: 1) those which induce selfcuring and 2) those which inhibit normal curing.

1) Conditions which induce self curing:— Sunlight— Fluorescent light after long periods

of exposure— Fire or flame— Extended storage at high temperature

(over 95°F)— Particles of rust— Strong acids, bases, or strong

oxidizing materials— Metal containers— High shear pumps

2) Conditions which can prevent ink fromnormal curing:— Excessive oxygen— Foreign particles of dust— Too thick of an ink layer— Old or dirty lamps and dirty reflectors— Insufficient energy to cure

Ink StorageBlack breathable polyethylene, polystyrene, orpolypropylene containers.

DisposalAs with conventional inks, UV inks should notbe poured in the sewage system or anywhereelse that would allow it to seep into the water

Glossary of Terms *

Acrylate: Chemical materials, usually mono-mers and oligomers, which contain the group-ing CH2=CHC-O-.

Buna-N/Buna Nitrile: A roller or blanket com-pound that is generally suitable for use with UVand conventional inks.

Catalyst: Any material which aids in comple-tion of a chemical reaction without itself be-coming part of the product.

Crosslinking Agent: A reactive chemical whichwill form bonds between other molecules in aformulation.

Cure: Conversion of a material from a rawstate to a finished and useful condition bychemical reaction.

Draize: Measurement of skin irritation. Thescale used ranges between 0-8, with 0-4considered mild and 8 considered severe.

EPDM: Ethylene Propylene Diene Monomer isa compound used to manufacture rollers andblankets, exclusively for UV printing.

Focal Distance: The distance from a lamp'sreflector at which peak energy can be ob-tained.

Free Radical: A reactive species having anunpaired electron which initiates a reactionwith a double bond. It is produced from itsstable paired state by energy absorption.

Inert Atmosphere: The blanketing (usually fromair) with a nonreactive (inert) gas, commonlynitrogen.

Mercury Lamp: Lamp in which light is gener-ated through the presence of mercury vapor.Most UV lamps are mercury vapor lamps.

Monomer: A molecule of relatively low molecu-lar weight capable of combining with itself orother similar molecules to form a polymer.

Nanometer: A unit of distance commonly usedin measuring wavelengths in the electromag-netic spectrum.

Oligomers: A lower molecular weight resin orpolymer which is used in an energy curableformula.

Oxygen Inhibitor: The effect of oxygen to termi-nate or retard the rate of polymerization.

Ozone: A form of oxygen that occurs when highenergy electrical discharge is present: O3

Photoinitiator: A molecule which, when exposedto a specific wavelength of energy, forms areactive species which starts the chain reactionto cause polymer formation.

Polymerization: A chemical reaction usuallycarried out with a catalyst, heat or energy, inwhich two or more reactively simple compoundscombine to form a macromolecule.

Reactive Diluent: A chemical which serves twopurposes in a formulation: 1) thinning or viscos-ity reduction and 2) providing reactivity withother ingredients.

Shelf Life: The amount of time a material maybe stored under specified conditions with nosignificant change in properties.

Thixotropy: A property of a liquid whereby itsviscosity decreases upon application of shearand increases when shear is removed.

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Thorough Cure: The curing of the bulk of a material down to and including the material substrate interface as opposed to a surface cure where only the material/air interface is cured. Ultraviolet Light: The light emitted in the 200 - 400 nanometer wavelength range. * Glossary of Terms adapted from the UV/EB Curing Primer by RadTech International North America. Used with permission.

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