Look around you—on store shelves, in your home—and you’recertain to see material that’s been printed by flexography. Thoughoften taken for granted, packaging is everywhere, and so, too, isflexography; it prints candy wrappers, shopping bags, corrugatedboxes, milk cartons, gift wrap, wallpaper, and many other goodsand packages. Printing on packaging is essential to businessesaround the world. In fact, graphics on packages provide some of the most important advertising for the products themselves.Flexography’s soft compressible plates, fast-drying inks, and its simple, efficient inking system make it possible for manufacturersto reproduce high-quality graphics on a wide variety of surfaces.

Over the last decade, the use of the flexographic printing processhas been growing approximately eight percent a year, a rate unparalleled by any other printing technology. Although some of this growth can be attributed to a greater need for packaging,flexography is increasingly used in markets traditionally served bygravure and offset lithography. Since advances in technology havesignificantly improved flexography’s ability to print accurate type,color, and halftone images, manufacturers and print buyers are recognizing flexography as a high-quality, economical alternative to gravure and lithographic printing.

This booklet describes the flexographic printing process from startto finish, including design, color, and prepress considerations.Understanding the requirements of flexography helps ensure thatdesigns will look their best, and will aid in the communication between print buyers, in-house prepress departments, service bureaus, and printers.

Cont

ents

1

2 Flexographic Markets

4 Traditional Printing Processes

6 Flexographic Technology

8 Flexographic Plates

9 Plate Elongation & Distortion

10 Substrates

11 Color Capabilities

12 Trapping

13 Type

14 Color Management

15 Dot Gain

16 Halftones & Screening

18 Step-and-Repeat & Die-Cutting

19 Prepress Output

20 Proofing

21 Prepress Checklist & The Press Check

22 Glossary & Index The terms printed in red

throughout this guide can

also be found in the glossary.

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2

The use of flexography is grow-ing in popularity in today’sprinting markets, where shortrun, low-cost, and high-qualityare crucial to success. A look at the development of flexography revealsa printing technology and culture thathas been willing and capable of changein response to the needs of the packag-ing industry. An evolutionary process of improvements in materials andequipment, rather than a single discov-ery, has led to flexography as it isknown today.

The first use of soft compressible platescan be traced back to the late 1880s,when letterpress printers needed to finda way to print kraft paper grocery bagsand corrugated boxes. The materialswere rough in texture, and did not respond well to the ink transfer pressureof hard letterpress plates. To solve theproblem, printers began creating platesfrom rubber, rather than from wood orlead. This quickly became the dominantmethod for printing corrugated, andalso grew steadily in the bag printing industry. In 1914, the Interstate Com-merce Commission approved the corru-gated box as a shipping container, a decision that began a new growth periodfor flexography.

Clear Packaging

In the early-to-mid 1920’s, flexographicprinters responded quickly to the intro-duction of cellophane as a clear packag-ing material. White inks were developed,drying systems were improved for cello-phane’s non-absorbent surface, and presstension systems were refined to handleits caliper and weight. Approximatelyten years later, polyethylene was intro-duced, and went on to become the mostcommonly used material for clear, flexi-ble packaging.

Market Categories

Corrugated

By far the largest market for flexography,corrugated is printed on sheet-fed presses.Fast drying water-based inks, the soft, conforming plate, and light impressionpressure make flexography well suited forprinting corrugated boxes in large quantities.

The use of the flexographic process has continued to grow in all packaging markets, including those that have traditionally used gravure and lithographic methods.

Flexible Packaging

Most flexible packaging uses non-absorbentpolymer film, including bread bags, snackfood bags, candy wrappers, pouches, andtextile wrap.

Gift Wrap and Wallpaper

A continuous repeat allows the printing ofproducts such as wallpaper and gift wrap.Design rolls, which do not have a plateseam, are used to print a continuous back-ground color.

Envelopes

Flexography is used to print many kinds of envelopes, including those for directmail, sweepstakes, general mailing, andovernight delivery. The security printingon the inside of many envelopes is oftenapplied by flexography.

Folding Cartons

Although folding cartons, including cereal,detergent, and cosmetic boxes, are printedby both the lithographic and gravure pro-cesses, flexography has recently increasedits market share due to improved quality.

Rigid Paper Boxes

Rigid paper boxes, or pre-formed boxesare used for bakery products, shoes, andneckties.

3

Origins of the Name

Originally, flexography was known as aniline printing, a name taken fromthe aniline dyes used as colorants for the ink. Aniline dyes, however, wereconsidered toxic and eventually bannedfor use on food packaging. New inkswere developed as replacements, but the name remained until 1951, whenFranklin Moss, a leader in packageprinting, started a campaign to changeit. He asked aniline printers and suppliersfor suggestions, receiving over two hundred. Of those, three finalists wereselected: permatone process, rotopakeprocess, and flexography. After a vote,the process came to be known as flexog-raphy in 1952.

In the United States, the Clean Air Actof 1980 began a development in flexog-raphy toward environmentally friendlyprinting using low-solvent and no-solvent inks. Today, flexography is often chosenbecause of the ability to print with cleanwater based or solventless ultraviolet inks.

Today the process continues to adapt.As the technology is refined, qualitycontinues to increase, making flexogra-phy the leader in packaging graphics applications.

Paper Grocery Bags

The paper bag is the original flexographicproduct. In the late 1800’s flexographyevolved from the need to apply graphics to plain brown grocery sacks. The evolutioncontinues today.

Plastic Carrier Bags

Flexography can add advertising andgraphics to plastic bags that are carried by customers in stores.

Milk Cartons

Approximately 90% of all milk cartons are printed using flexography.

Newspapers

In the United States alone there are between 35 and 40 newspapers using the flexographic printing process for theentire paper. Many newspapers use flex-ography to print the Sunday comics.

Tags and Labels

The fast drying fluid inks used by flexogra-phers allow inline die cutting immediatelyafter printing. The quality of many flexo-graphic labels is equal to or better thanthat offered by lithography or gravure.

Pre-printed Linerboard

Pre-printing linerboard allows high-qualitygraphics to be placed on corrugated containers.

Trad

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4

Offset Lithography

Gravure

Flexography

The three most widely usedprinting processes in use todayare offset lithography, gravure,and flexography. Printing pressesfor each method differ primarily in design of the image carrier or printing

plate, the ink, and the ink delivery system to the printing plate.

Offset Lithography

Widely used in the publication indus-try, offset lithography presses printmagazines, catalogs, and daily newspa-pers, as well as annual reports, advertising,and art reproduction. Offset lithographycan also print paper-based packaging,such as cartons, labels, and bags.

Offset lithography is a planographic

process, meaning that the printing plateholds both the image and non-imageareas on one flat surface or plane. Onmost offset presses, image areas on theplate are chemically treated to attract thelithographic paste ink, while a fountain

solution or ink repellent chemicaltreatment protects non-image areas frominking. From the plate, the image is firsttransferred to a blanket (hence the termoffset), and then to the paper or othermaterial, known as the substrate. Todry, most lithographic inks require acertain period of time or an applicationof heat.

Gravure

The gravure method, sometimes knownas roto-gravure, is used on a wide vari-ety of substrates, including vinyl floor-ing, woodgrain desktops, and paneling.It is the second most often used processin Europe and the Far East, and thethird in the United States. Gravure isused to print high-volume productssuch as packaging, magazines and theadvertising inserts found in newspapers.In addition, offset versions of gravurepresses are used to print labels or logos

5

Traditional Printing Processes

Magazines, newspapers, advertising pieces,annual reports, cerealboxes, bags, tags &labels

Coated & uncoatedpapers, newsprint,some polymer packaging films

Moderate to heavy

300,000 to 400,000maximum impressions

Sheet-fed: to 60"Web: 11" to 60"

Standard format withlimited repeat length

Product dependent:Magazines: 2,500 fpmSheet fed: 12,000 impressions per hour

Paste inkOil & soy basedHeat set & non-heat setWet trapping

65-300 lpiMost common: 133-150 lpi

3-5%

Midtones: 20%

Magazines & catalogs, Sunday supplements, candywrappers, cerealboxes, snack foodbags, vinyl flooring

Coated & uncoatedpapers, newsprint,paperboard, foil, metallized paper,polyethylene vinyl,polypropylene, cellophane,polystyrene

Heavy

6 to 7 million impressions average;longer withrechromed cylinder

2" to 144"

Infinitely variable repeat length

Product dependent:Magazines: 3,000 fpmBread bags: 500-900 fpmVinyl flooring: 50 fpm

Fast drying fluid inkSolvent & water-basedDry trapping

120-300 lpiMost common: 150 lpi

3%

Midtones: 23-26%

Newspapers, phone directories, corrugated containers, bread bags, cereal boxes, milk cartons, gift wrap

Coated & uncoated papers, newsprint, paperboard, corrugated board, foil, metallized paper,polyethylene vinyl,polypropylene, cellophane, polystyrene

Light

1 to 2 million impressions average

Narrow web: 6" to 24"Wide web: 24" to 90"120" for corrugatedpresses

Variable repeat length

Product dependent:Toilet tissue: 3,000 fpmBread bags: 500-900 fpmPressure sensitive labels: 100-300 fpm

Fast drying fluid inkSolvent & water-basedUV curableDry trapping

45-150 lpiMost common: 100-133 lpi

8-12%

Midtones: 20-25%

Typical

Uses

Substrates

Impression

Pressure

Plate Run-

Length

Press Width

Repeat

Length

Press Speed

(feet per

minute)

Ink

Screen

Ruling

Minimum

Printed

Highlight Dot

Dot Gain

OffsetLithography

Gravure Flexography

on medicine capsules and the “M” onM&M® candy.

Gravure is an intaglio process, in whichthe image area is recessed below thelevel of the non-image areas. The imageis etched or engraved in a cell formatonto a copper plate or copper-platedcylinder. By varying the size and depthof each cell, a printer using a gravurepress can vary tones. Often, after thecopper is etched or engraved, the plateor cylinder is plated with chrome to adddurability and increase its run-length.A fast drying ink fills the recessed cells,a thin metal strip called a doctor blade

clears the non-image area of ink, andthe image is transferred directly to thesubstrate under heavy pressure from arubber covered impression cylinder.

Flexography

Because its soft compressible plate con-forms to uneven surfaces, flexography is often used for printing on packagingmaterials, such as corrugated and paper-

board. The fast-drying fluid inks usedin flexography are ideal for such materi-als as polyethylene films, used for plasticgrocery bags. Flexographic presses areoften part of a manufacturing process, in which packaging is printed, folded,shaped, and die-cut.

Flexography is characterized as a relief

process. The image areas on the com-pressible plate are raised above the sur-rounding non-image areas. An ink metering cylinder called an anilox roll

applies ink to the raised areas. The plateis then moved into light contact withthe substrate to transfer the image. Theminimal pressure during image transferallows printing on material, such as cor-rugated board, that may be adversely affected by impression pressure.

6

Flex

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Tech

nolo

gy Flexographic Ink Delivery System

Characteristics of Anilox Rolls

Two Roll with Doctor Blade

Dual Doctor Ink Chamber System

Range: 140 to 1200 CPI. As cell count increases, ink delivered to plate decreases. As line screen resolution increases, CPI should also increase.

Range: 1.8 to 17 BCM (Billion Cubic Microns per square inch of cells). As CPIincreases, cell volume decreases.

Typical anilox cell angles are 30°, 45°, and 60°. A 60° angle allows for morecomplete ink transfer, and is the preferred cell angle. The screen angle of theprinting plate and the cell angle can combine to cause a moiré pattern, evenwith one color halftones. Moiré is avoided by angling separation screens.

Cell Volume

Cell Per Inch

(CPI)

Cell Angle

Application

line art

halftones at 65 lpi

4/c halftones at 133 lpi

Substrate

corrugated board

corrugated board

polyethylene bags

Cells Per Inch

200-280

360-400

600-900

Cell Volume

7-8.5 BCM

4.0-5.5 BCM

1.8-2.0 BCM

Flexographic printing units inuse today consist of three basictypes: the two roll unit, the two rollunit with a doctor blade, and the dual

doctor ink chamber system.

Two roll units are usually found on olderflexographic presses, and on narrow

web presses. Narrow web pressesequipped for process colors often usethe two roll unit with a doctor blade,and more modern wide web pressesuse the dual doctor ink chamber system.

Each type of flexographic press uses ananilox roll. The surface of every aniloxroll is engraved with a pattern of tinycells, so small they can only be seenunder magnification. The size andnumber of these cells determine howmuch ink will be delivered to the imageareas of the plate, and ultimately to thesubstrate. An anilox roll is either copperengraved and then chrome-plated, orceramic coated steel with a laser engravedcell surface.

Anilox rolls are carefully selected forspecific types of printing, substrates,and customer requirements. Often theflexographic printer will perform testruns to determine the ideal anilox forproducing the desired ink distributionfor halftones, spot color, and solids.

The design of the flexographic printingunit enables press manufacturers tobuild presses in any one of three config-urations: the stack press, the inline

press (including corrugated presses),and the common impression cylinder

press. Each configuration can beequipped with any of the basic printingunits, depending upon the needs of theflexographic printer.

On a two-roll flexographic printing unit,the rubber covered fountain roll rotatesin a fluid ink bath, dragging ink from thepan to cells of the anilox roll. The softrubber fountain roll is held in tight con-tact with the anilox roll. As the anilox rotates past the nip point, the fountainroll wipes excess ink from non-cellareas. Once past the nip point, each cellis filled with ink, and a measured, repeat-able amount of ink is available to theprinting plate. The metered anilox roll is moved into light kiss contact with theimage areas of the plate, and the plate

cylinder is moved into kiss contact withthe substrate to transfer the image. Thesteel impression cylinder supports thesubstrate. When a thin metal or poly-ethylene doctor blade is used with atwo-roll unit, the nip point between thefountain and the anilox roll is opened toallow ink to flood the anilox and fill thecells. The doctor blade comes into con-tact with the anilox to clear excess inkfrom non-cell areas. With a dual doctorink chamber, the fountain roll and inkingpan can be eliminated; ink is delivereddirectly to the anilox through an enclosedchamber.

7

Corrugated Press• Same configuration as the inline press• Sheet-fed; widths up to 120"• Usually no more than 4 colors• Limited to one-sided printing• Less accurate registration capabilities

Repeat Length

Press Configurations

Common Impression Cylinder (CIC) Press• 4-8 color units• Limited to one-sided printing• Ideal press for hairline register at high speeds on stretchable

films• Longer make-ready times required because printing units are

more difficult to access

Stack Press• 1-8 color units• Some presses can print on both sides • Traps should be no less than 1/64" for thin films • Often used inline with other converting operations such

as lamination, rotary and flatbed die cutting, and sideseal bag converting.

Inline Press• Up to 12 color units• Can print two sides with the aid of a turn-bar• Used for printing thick substrates such as paperboard• Not recommended for printing thin packaging film • Often used inline with other converting operations such as

lamination, rotary and flatbed die cutting, and sideseal bag converting.

Plate cylinders with different diameterscan be mounted on many flexographicpresses, allowing for variable repeat

lengths. Printing a roll of packaging, suchas gift wrap, uses a continuous repeat,where the same set of images is repeatedmany times on a continuous stream ofsubstrate. To avoid the plate seam, imagesmay require nesting, an arrangement thatcreates a staggered effect. Staggering im-ages gives the appearance that the designis continuous, no matter where the sub-strate is cut.

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Molded Rubber

Photopolymer Plates

Laser Ablated Plates and Design Rolls

Printing plates used on modernflexographic presses are producedin three different ways: molding rubber,exposing and processing photopoly-

mer, and imaging with lasers. Whilemolded rubber plates have been usedsince the 1930’s, photopolymer plates,introduced in the 1970’s, generally pro-vide higher resolution and more accu-rate color registration. Direct-to-platelaser imaging, called ablating, is avail-able for both materials. Selection of aparticular type of plate depends on thepress, the plate cylinder inventory, andthe customer’s requirements, such asresolution, registration, and cost.

Molded Rubber

Molded rubber plates are created in amultistep process that involves exposingand etching a magnesium plate, makinga mold, and then placing the image onthe rubber plate using a molding press.

Photopolymer

Light-sensitive photopolymer is suppliedin either solid sheets or in a thick liquidstate. The image area of the plate is exposed through a film negative. Liquidphotopolymer, about the consistency of honey, solidifies when exposed to ul-traviolet light. After exposure, the non-image area is removed by processing.

Laser Ablated Plates

Some platemaking machines can trans-fer images directly from the computerto the plate, a process known as direct-

to-plate that avoids the production offilm. Some photopolymer plates can bedirectly imaged by lasers and then con-ventionally processed. A design roll is a cylinder covered with rubber or photo-polymer and molded or imaged by alaser. Design rolls can provide a truecontinuous repeat with a continuousbackground color. Laser ablated platesmust be nested to hide the plate seamfor the appearance of continuous repeat.

• Molded rubber plates shrink when theyare removed from the molding press.Plate films should be adjusted to com-pensate for shrinkage, which is typically1.5%-2.0% in the direction of the rubbergrain, and .5%-1% across it. Exactshrinkage amounts should be commu-nicated between production artists andplatemakers.

• Line screening is limited to 120 lpi.

• Registration can be more difficult thanwith photopolymer plates.

• Nesting is required for the appearanceof continuous repeat.

• It is difficult to mold accurate rubberplates larger than 24" X 36". Larger designs must be placed on multipleplates for each color.

• Line screening is at least 150 lpi and canbe as high as 200 lpi.

• Nesting is required for the appearance of continuous repeat.

• Positioning and register devices on most modern flexographic presses aredesigned for one-piece photopolymerplates.

• Direct-to-plate laser imaging is available.

• Line screening is limited to 100 lpi fortone reproduction, but can be 200 -300lpi for tints.

• Film is not required.

• Design rolls can provide a true continu-ous repeat with a continuous back-ground color.

• Plates or design rolls imaged directly on the cylinder do not require compen-sation for plate elongation.

• Laser ablating is available for both rubber and photopolymer.

Plate Types

Plate Elongation

9

Plat

e Elo

ngat

ion

& D

istor

tion

Distortion

Expected result

Plate elongation occurs around the cylinder

Printed piece with-out compensation for elongation

After plate mounting

Before plate mounting

Spreading Stretching

Platecenterline

Plate

� x 2(T)

RL

3.1416 x 2(1.27")

18.8"= 0.0424"

� = 3.1416

For every linear inch of plate used around the cylinder or curve direction, the images will increase at the rate of 0.0424".

Design measures 12" in the curve direction.Calculate plate elongation: 12" x 0.0424" = 5.09"

The image is distorted to compensate for plate elongation. Film is output to 11.491" (12" – 5.09") or 95.7% in the curve direction, and 100% in the non-curve direction.

T = 1.27"; plate thickness with mounting tapeRL = 18.8"; repeat length of plate cylinder

12"

12"

Final design prints correctly since plate elongation has been compensated for.

11.491"

12"

When designing images forflexographic printing, it is important to understand the effects of plate elongation. Becauseflexographic plates are made with softmaterial, they tend to stretch whenmounted on the plate cylinder, some-times distorting images and text. A cir-cle, for example, may be stretched tolook more like an oval.

Fortunately, special flexographic soft-ware can compensate for plate elonga-tion by slightly distorting images.Distortion is usually performed withinthe flexographic software application or at the RIP stage before the film is imaged. The amount of distortion depends on the thickness of the plateand the mounting tape used to fastenit, and on the circumference of thecylinder (the repeat length). In general,thicker plates and shorter repeat lengthsincrease the elongation.

To be sure that images will be printedwith the correct size and shape, the design should be output to film afterplate thickness has been determined and the proper distortion factor hasbeen applied. Improperly calculated distortion may also cause misregistration.

Direct-to-plate imaging, which is becom-ing more widely available, avoids theneed for distortion if the imaging is applied directly on a design roll, or on a plate already mounted on the cylin-der. Because the image is applied to acurved surface, no stretching occurs.

As the soft plate wraps around the cylinder, it canelongate, stretching images, halftones, and text acrossthe curve dimension. Without compensation for plateelongation, images will not print as designed. In theexample, if no compensation is applied, the sun imageis printed as an oval and the vertical lines on each sideare lengthened.

Special flexographic software can compensate for plate elongation by adding distortion,using a basic formula, as shown in the following example.

10

Subs

trates Substrate Characteristics

Paper/

Paperboard

Polymer

Films

Multilayered/

Laminations

kraft linerboard:

corrugated, for boxes

coated kraft:

corrugated, for boxes

solid bleached sulfate (SBS):

folding cartons

recycled paperboard:

folding cartons

coated paper:

labels, gift wrap

uncoated freesheet paper:

paperback books

polyethylene (PE):

dry cleaner bags, bakery,textile bags

polypropylene (PP):

snack packages, candywrappers, cookie packaging labels

polyvinyl chloride:

vinyl films, labels, wall coverings

metallized papers:

gift wraps

metallized film:

snack food bags

polyethylene coated solid

bleached sulfate:

milk cartons

ColorDependent upon substrate material; substratecolor will significantly influence ink.

Whiteness/BrightnessThe strength of white or color of a substrate.

OpacityAmount of light transmitted through the substrate. A lower opacity allows more lightto pass through.

SmoothnessSmoother substrates allow higher lpi; rough,irregular surfaces require much lower lpi.

AbsorptionDetermines how ink dries and spreads. Lowabsorption produces drying at the surface, increasing color saturation and decreasingdot gain. Higher absorption increases dot gain.

GlossReflective quality of the substrate. Gloss can be increased with varnish or laminationand can be decreased with matte or low-glossfinishes.

CaliperThickness of a substrate, as measured by amicrometer.

White, brown kraft, a varietyof colored papers.

Increases with bleached &coated papers. Decreaseswith greater amounts of re-cycled fiber. Optical bright-eners can be added.

Thin, lightweight papershave lower opacity & aremore likely to have ink showthrough.

Newsprint, corrugated liner-board & paperboard are rela-tively rough; calendered &coated papers smoothest.

Newsprint, corrugated liner-board & paperboard are veryabsorbent, calendered; coat-ed papers are less absorbent& exhibit high ink hold-out.

Calendered & coated papersare high gloss; corrugatedlinerboard, newsprint & paperboard are low gloss.

Range: .002" to .010"; paperboard � .010". Thin papers more consistent incaliper; paperboard more inconsistent.

Clear, white or colored.

Determined by the opacity of white film. Clear films require the use of a whiteplate.

Low for thin, lightweight papers, which are more likely to let ink show throughon reverse side.

Smooth printing surfaces;ink adhesion is sometimes a problem.

Non-absorbent, with no dotgain.

High for most films, butfilms can be produced with a matte finish.

Ranges from .00065" to.006". Thin films may stretch;inconsistency in caliper cancause misregistration andwrinkling.

Determined by the top-mostlayer.

Determined by the top mostlayer. Foil & metallized sur-faces require the use of awhite plate.

Higher with multiple layers of material.

Determined by the top-mostlayer.

Usually low, but determinedby the substrate used as aprinting surface.

Determined by the top-mostlayer.

Increases as layers areadded. Thin layers may belaminated together to ob-tain the required thickness.

Flexography is ideal for printingpackaging materials because thesoft plates can transfer ink to manydifferent kinds of substrates—anythingfrom corrugated board to candy wrap-pers. The quality of a printed product is determined not only by the type ofplate, but also by the substrate itself.Different substrates allow varying degreesof ink absorption, gloss, brightness, andcolor definition. The chart on this pagelists the characteristics of some commonsubstrates.

Colo

r Cap

abili

ties

11

White Plate

Multicolor Options

Reverse-Side Printing

In flexography, opaque spot colors areprinted in the order of lightest to darkest.Process color inks are made from trans-parent pigments and can be applied in any sequence. For transparent substrates,white ink is printed first to provide a background for colors.

In order to place colors on a transparent substrate, a solid white ink is printed first to create a reflectivebackground that improves the color intensity. Thecolored inks are then printed on top of the whitebackground.

An exception to the rule of light-est to darkest printing occurswhen a spot color or line art job calls for reverse-side print-ing, sometimes called “backprinting.” Styrofoam productsare often decorated by laminat-ing a reverse-side printed film.Some snack food packaging isalso done this way.

Because the appeal of packagingis significantly enhanced bycolor, flexographic presses com-monly offer six and eight colors, andeven as many as twelve for limited applications. Designers can choose froma number of different combinations, including multiple spot colors and HiFi

printing, which is a method of increas-ing the color gamut by printing six orseven process colors.

Most flexographic inks consist ofopaque or semi-opaque pigments. Toensure proper ink coverage, the spot colors are usually printed from lightestto darkest. Process color inks are madefrom transparent pigments and can beapplied in any sequence. Transparentsubstrates, such as polypropylene, requirea white backup plate provided by a“choke” plate, as a background for col-ors; otherwise, colors would appear flatand translucent.

Another technique used for applying inkto transparent substrates is reverse-side

printing. The image is laterally reversed,and colors are printed instead fromdarkest to lightest; the packaging is thendisplayed from the non-ink side of thesubstrate. This provides a scratch proofsurface to the ink layer, and a glossy fin-ish. In some cases, a water-based ink isused for reverse-side printing lamina-tion. Paper or styrofoam plates are oftendecorated by laminating a reverse-sideprinted film layer to the plate.

Corrugated containers have historicallybeen only one color on brown kraftpaper linerboard, but more designers aretaking advantage of multiple spot andfour-color process capabilities. In somecases, printing is done directly on a whiteor clay coated corrugated linerboard,avoiding the costly practice of applyinglabels to achieve high quality graphics.

Trap affecting colors

Nailheads

12

Trap

ping

Spread lighter color Choke lighter color

Choking and Spreading

Overprints and Traps

Trapping is a technique of over-lapping colors to avoid unsightlygaps created by misregistration.Small variations in the placement ofcolor, called misregistration, can becaused by substrate handling and ten-sion problems on the press, irregularplate elongation from one color to thenext, inaccuracies in plate mounting,plate bounce, and limited register capa-bilities, especially with molded rubberplates. A test run, called a fingerprint-

ing analysis, can determine the registra-tion tolerances.

When designing packaging for flexo-graphic printing, it is best to avoid therequirement for tight registration, to design images with dominant colorsprinted on top of lighter ones, and toavoid trapping on gradations. Typically,a designer will build traps into the file if the design is simple, using options in publication or illustration software;more complicated designs require thehelp of service bureaus and special trapping software programs, such asTrapwiseTM from Luminous Corporationor DK&A Island TrapperTM.

Trap widths on narrow web pressesshould be set at a minimum of 0.005";some presses require as much as 1/32"(0.031"), which is large compared to average traps of 0.002" - 0.005" for off-set lithography. A typical trap width for polyethylene printed on a wide web press is 1/72" (0.014"), though ifan objectionable dark trap line is created,the width may need to be cut in half.Trapping for linerboard or corrugatedcardboard may require a trap width of1/64" to 1/8".

Traps are created by spreading or choking graphic elements, depending on adjacent colors. When a lighter element appears against a darker background, the lighter color isspread into the darker color, slightly increasing the size of the graphic element. When adarker element appears against a lighter background, the knockout is choked by slightlyfilling it with the lighter color. Both methods create a small overlap of ink colors, calledthe trap width. This width depends on the thickness and size of type, the adjacent colors,and the registration capabilities of the press. Script, serif fonts, or small type can bespread or choked only small amounts before the shapes are compromised. In general,light and dark colors allow for greater trap widths than colors that are similar.

Printing inks on top of each other is called overprinting. In flexography, one ink can be printed on another only after the first has been completely dried or cured. For this reason, flexographic presses use dry trapping, where the printer must allow for drying. For substrates like clay-coated liner, or non-absorbent packaging such as polymer film,drying time can be a problem. Overprinting a second color when the first is not dry cre-ates an unattractive blotchy effect (often called nailheads), especially on large solids.Excessive trapping can cause such problems and can slow down the printing process.

13

Typographic Guidelines

Type Weight

Type

4 point minimum positive san serif type for narrow web presses

6 point minimum positive san serif type for wide web presses

8 point minimum positive serif type for wide web presses

Kerning may cause squeezing across cylinder, avoid tight linespacing

Kerning may cause squeezing across cylinder, avoid tight linespacing

6 point minimum reverse type for narrow web presses

9 point minimum reverse type for wide web presses

EDIENTS: FILTERAR, CORN SYRUP

A AND LOWFAT CESSED WITH ALIN, NATURAL VA

EDIENTS: FILTERAR, CORN SYRUP

A AND LOWFAT CESSED WITH ALIN, NATURAL VA

All positive text should be printed in a single color if possible PMS 407

All positive text should be printed in a single color if possible 6m 8.5y 27.5k

Substrate

Ink spreading

Deforming plateOver-impression

Pressure

Ink

In flexography, thesoft plate compressesin the printing nip,causing the fluid inkto flow slightly out-ward from the imagearea. Thus the weightof type may appear toincrease, and reversetype may fill-in.

Made in the U.S.A.

47c

94m

15y

5k

47c

94m

15y

5k

Letterspacing and/or linespacing may increase slightly from plate elongation.

Avoid placing fine type on the same color platewith line work and solid printing areas.

Avoid reversing type out of two or more colorsunless a dominant color outline is used.

Specify type accurately to the service bureau or prepress department.

In flexography, printing consis-tently well-defined type iscomplicated by the soft plate,irregular substrate surface, andthe fluid ink. Ink tends to spread out-ward, sometimes obscuring the defini-tion of small point sizes or the fine detail of certain letter shapes. Reversetype, which uses the substrate or a back-ground color to define the letter, tendsto get filled in.

To help compensate for the typographicweight gain, it is possible to use thetrapping techniques of spreading onpositive type and choking on reversetype. Software programs, such asMacroMedia FreeHandTM and AdobeIllustratorTM, let the designer adjust thethickness of type. Some compensationcan be done by choosing either a lighteror bolder face. For example, if mediumpositive type is desired, use a lighterweight face; if a medium reverse type isdesired, specify a bold face. When possi-ble, sans-serif fonts should be used. Ingeneral, larger point sizes produce moreconsistent type.

Letterspacing must also be considered.Letters squeezed together for a denserappearance with offset lithography maymerge together unacceptably in flexog-raphy. Ideal letterspacing keeps lettersclose enough together so that they lendsupport to each other while under thepressure of the printing nip, but sepa-rated enough to avoid merging.

Test Targets

14

Colo

r Man

agem

ent The wide variety of substrates,

lack of standard ink hues, andunique dot gain characteristicsall contribute to the difficulty of com-municating and reproducing color bythe flexographic process. Color Manage-

ment Systems (CMS), such as Agfa’sColorTune 3.0 are software systemsused to ensure color consistency amongdifferent input and output devices sothat printed results match originals. The use of these systems aid in the color communication process by corre-lating colors on computer monitors and proofing devices with the actualor expected color results from the print-ing press.

Because a color monitor can produce amuch wider gamut of colors than theinks on a printing press, the designerneeds to know the range of printablecolors available on the computer. Tofind this range, a color specialist can runa CMS test on the flexographic printingpress under controlled conditions, usingthe same ink, plates, mounting tape, andanilox rolls required for the actual pro-duction run. Since each substrate affectscolor in a different way, a new test needsto be run for each new type of material.

The results of the test are entered intothe CMS software, which sets up cali-bration tables and builds press profiles.Digital cameras, scanners, monitors, andproofing devices are all adjusted by theCMS, based on the colors printed by theindividual press. Input devices such ascameras and scanners, and prepress out-put devices including monitors andproofing systems are adjusted accordingto the predicted outcome on press.

ABCDEF

ABCDE

GHIJKLMN

A B C D E F1 2 3 4 5

1 2 3 4 5 6 7 8 9 10 11 12 13

1 2 3 4 5 6 7 8 9 10 11 12 13

12

34

56

I T8 .7 /3

1 2 3 4

High total ink amountto check density

Neutral greys printed with CMY(and K in some cases) to checkgrey balance

CMYK density wedgesto check dot gain

Solid CMYpatches

Saturated colors withno black

Saturated colors with20% black

Shadows

Color Management Systems build profiles by analyzing standard color data from testtargets. The IT8 series of test targets can be used to calibrate prepress input devices(such as scanners), and output devices (such as proofing devices), monitors, and thepress itself. The IT8 7/1, IT8 7/2, and the IT8 7/3 (shown above) test targets all contain the same standard color information, but each uses a different format.

IT8 7/1 is a reflective color test target input to calibrate scanners for reflective art in acolor management system.

IT8 7/2 is a transparency of the same format as IT8 7/1, but used to calibrate scanners for reading transparencies, rather than reflective art.

IT8 7/3 is a digital file of the same format used to calibrate imagesetters. To build a pressprofile, the imagesetter is calibrated and the IT8 7/3 file is output to film. Plates are madeand mounted, and the IT8 7/3 is then printed under the actual production conditions.

Printed samples are measured for density, dot gain, and colorimetric values, and the resulting data is entered into the color management system. CMS software then recali-brates monitors, digital proofing devices, and imagesetters to correlate the output ateach of these devices with the expected output from the actual press run.

There are several color measurement tools used by flexographers to measure printedsamples. Used primarily in the press room, the reflection densitometer can only trulymeasure reflectance. It is used by the flexographer to measure solid ink density for pro-cess color printing. The colorimeter, important because it assigns numerical values to all colors in the gamut, measures hues printed as either spot colors or screen tint combi-nations of CYMK. The spectrophotometer is most useful for ”fingerprinting“ specifichues of CYMK and base colors used for ink mixing.

Dot

GainDot Gain in Flexography

Impression Pressure

Inks

Substrates

Plate Durometer

All printing processes are sub-ject to the unavoidable occur-rence known as dot gain. As dotsare transferred from film to plate, theytend to grow in size during light expo-sure. When an ink dot is transferredfrom the plate to the substrate, it canincrease in size once again as the inkspreads during absorption. A dot thatbegan as 50% on film can grow to 51%on the plate, and eventually print on a flexographic press as a 65% or greaterdot. The fluid ink and compressibleplates used in flexography tend to increase dot gain, but it varies accordingto the type of press and the substrate.Smooth non-absorbent films and coatedpapers will have less dot gain than absorbent and irregular surfaces, such as uncoated papers, newsprint and cor-rugated liner board.

Dot gain, however, is often consistentand predictable. Image or color separa-tion software can adjust dots based onmeasurements supplied by the printer.Typically, the printer performs a finger-printing analysis, which provides dotgain information to the color separatoror desktop designer. The IT8 chart onpage 14 shows an example of a test tar-get used for a press fingerprint. Byprinting such a target under controlledconditions, dots can be adjusted in thecolor separation films. In addition, cali-bration packages built into raster imageprocessors (RIPs), such as Agfa Calibra-tor, can also make adjustments.

Even though ink is transferred underrelatively light pressurein the printing nip, thesoft flexographic platedeforms slightly andcompresses duringimage transfer. Thiscauses ink to spread, increasing dot gain.

Because harder plates do not com-press as much as softer plates, theyproduce less dot gain. Softer plates,however, transfer solid images morecompletely.

Dot gain can be minimized by usinga thin (0.002"-0.005") capping layersurface with a higher durometerthan the supporting plate material.Dot gain can also be reduced bymounting the plate with compress-ible tape or a blanket that absorbspressure.

An instrument called a Shore A scale measuresplate hardness, which is called durometer. Theimage on the left shows the scale measuring asoft plate; on the right it measures a harder plate.

A higher viscosity ink will notspread as quickly as one withlower viscosity. The spreading,or flow-out, of a low viscosityflexographic ink occurs as it istransferred to the substrate andbefore it dries, contributing todot gain. By comparison, litho-graphic ink is a thicker, pasteconsistency, and is not prone toexcessive flow-out.

The printing surface or finish of a substrate also influences dot gain. When ink is applied to smooth non-absorbent films and coated papers it tends to spread very little,preserving the dot shape. With more absorbent and irregular printing surfaces, such asuncoated paper, newsprint, and corrugated liner board, the paper fibers act as a wick,absorbing the fluid ink and causing it to spread beyond the dot shape and pattern.

15

16

Half

tone

s & S

cree

ning Halftone Dot Shape

Screen Tints and Gradations

Square dots at 50% Stochastic dots at 20%

Symetrical rounddots at 65%

Asymetrical round dots at 75%

Asymetrical round dots reversed at 80%

Offset lithography

Flexography

Throughout its history, flexog-raphy has been printing qualityline art and spot colors on awide variety of substrates. How-ever, it is the recently improved capabili-ty of high-quality, economical four-colorprocess printing that has given flexogra-phy an edge over other processes forpackaging applications.

The Halftone Dot

In flexography, the shape of the halftonedot used to reproduce a continuous toneimage can significantly affect the densityof the image. Halftone dots can be gen-erated in a number of shapes, includingsquare, elliptical, octagonal, and bothsymmetrical and asymmetrical dots. At50% coverage, for example, square dotsproduce a pattern resembling a checker-board, with individual dots just begin-ning to join at their corners. Whenplates are created from film, dot gain increases the joining of the dots, whichcauses sudden jumps in density in theprinted image, rather than a smooth,continuous transition.

To minimize the density jumps, printerscan use other kinds of dots that remaindiscreet and retain their shape, even atcoverages of sixty and seventy percent. A round dot, or octagonal dot are oftenused. Though most design software can specify round dots, selection of dotshape should occur early in the processto avoid choosing a shape not availablein the RIP, imagesetter, or platesetter.

Conventional Screen Ruling

Selection of proper screen ruling, whichis critical to four-color process flexogra-phy, is often dictated by the type of sub-strate. Anilox cell count and screen rulingfor separations should be correlated for best results. The cells of the anilox,which ink a halftone plate, should belarge enough to produce appropriate

To minimize density jumps in halftones,round dots are preferred. Round dots donot touch until coverage is nearly 65%for the symmetrical round dots and 75%for asymmetrical dots. Dot gain is less at these higher coverages, and is moreeasily controlled or compensated for.

Highlights

Most photopolymer plates are capable ofholding a 2% highlight dot. If plates aren’tproperly exposed, however, screen tints andhighlight dots less than 3% tend to drop out.Because the small dots of highlight areas aresubject to relatively large dot gain, it is impor-tant that any highlight limitations are dis-cussed with the printer before separationsare made. Although printers in offset lithogra-phy can print acceptable highlights using 5%film dots, flexographic printers may have toreduce a similarly bright highlight to 2%, tak-ing into account the additions of dot gain.

Gradations and Vignettes

Flexographic dot gain on highlights makes it difficult to print a fade-to-white gradationwithout a harsh break at the highlight edge.When designing images for flexography, it isbest to fade off the end of the design (ratherthan to white), or place a border at the high-light end of a vignette.

17

Line Screens and Cells Per Inch

Anilox Cell Angles and Halftone Screen Angles

30°60°45°

Anilox cell angle

Offset halftonescreen angle 7.5°from cell angle

65 lpi 280-360 cpi Corrugated

85 lpi 360-400 cpi Newspaper

133 lpi 500-600 cpi Flexible packaging

150 lpi 800 cpi Labels

To avoid anilox moiré, film or platescreen angles should be at least 7.5°away from the anilox cell angle. Cyan,magenta, yellow, and black screen angles should also be set at least 15°apart from each other.

The corrugated industry printshalftones screenedat 45, 55, 65, or85 lpi.

Flexographicnewspaper printersprint halftonesscreened between65 and 100 lpi.

Flexible packagingon film substratesis commonly doneat 120 to 150 lpi.

High quality labelprinters have thecapability of print-ing 200 lpi images.

Cells are engravedon an anilox roll atone of three angles: 30°, 45°, or 60°.

Screen Ruling

(lpi)

Cells Per Inch

(cpi)

Application

color strength, but not so large that thehalftone dots will dip into them like an inkwell. For conventional halftones,resolution is expressed as the number of lines of halftone dots per inch, alsocalled screen ruling or lpi. Higherscreen rulings produce higher resolutionimages because there are more dots persquare inch used to reproduce detail.Compare the images in a newspaper(low screen ruling) to a picture in amonthly magazine (high screen ruling).

Stochastic Screening

Stochastic, or frequency modulated

(FM) screening, can offer advantagesover conventional halftone screening.Stochastic screening eliminates the possi-bility of moiré, and also allows the flexographic printer to use HiFi color,which involves the application of six orseven process colors.

Dot size used for stochastic screening,however, is extremely small, comparablein size to the highlight dot of conven-tional screening. Since flexography issubject to significant dot gain, stochas-tic screening should only be used afterthe printer and color separator have performed press fingerprints to deter-mine the ideal dot size and accuratecompensation for dot gain.

The number of lines per inch on theplate should be no more than 25% ofthe cells per inch on the anilox. Ideally,the anilox should contain a minimum of 4 cells for every halftone dot.

Step

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18

Step-and-Repeat

Die-Cutting

Plate Bounce

To save material costs and maxi-mize productivity, the packaging industry uses a printing technique calledstep-and-repeat. Different images,such as labels, are arranged on the plateto fill its repeat length and use the entirewidth of the substrate when printing.

Often, a technique called nesting willbe required. Images are strategically staggered in an arrangement that maxi-mizes the repeat length and avoids theplate seam. The plate ends are cut to accommodate the arrangement. Nestingcan give the appearance of a continuousrepeat, and is used for jobs where all theimages are part of a single roll, such asgift wrap.

In addition to maximizing substratearea, staggering images can also avoid aproblem called plate bounce. In flexo-graphy, images are on the raised areas of the plate, and can produce a bouncewhen coming into jarring contact with an anilox roll or impression cylin-der. Bouncing can cause print areas toskip or misprint if the bounce is awayfrom the impression, or areas of excessinking if the movement is toward theanilox roll.

After printing, most substrates are cut,folded, scored, sealed, or glued, often inline. In order for packaging to be pro-perly constructed, die-cutting require-ments must be exactly specified for boththe designer and the printer. A die-cutlabel or folding carton, for example,must have all graphical elements in thecorrect positions. Packaging engineersoften use Computer Aided Design

(CAD) systems to design folding cartons,corrugated containers, or rigid paperboxes; designers may also import theCAD layout to use as template for design.

Nesting images can maximize the plate areaand avoid the plate seamfor step-and-repeat print-ing. Layout and impositionsoftware offer step-and-repeat options for specificrepeat lengths and webwidths.

Bleeds To specify bleeds, the designermust know where the packaging will becut, folded, and joined. In general, bleedsextend beyond fold and cut lines, but theprecise amount of bleed depends on thepress.

Cut Areas When flexographic printers areconnected to inline flatbed or rotary die-cutting, the die must be held in registerwith the printed colors. Graphic elementsshould not be placed too close to cut areas.

Glue & Seal Areas To ensure sealing, glueareas should be free of ink and varnish,especially those sealed by heat.

Score Lines Die-cut folding cartons usual-ly fold at score lines, where the designershould make sure that registration is precise.

Varnish-Free Areas Areas that containvariable information, such as freshnessdates and product coding, must be free ofvarnish.

Windows Die-cut windows for folding car-tons or labels should be clearly indicated,but may not be available on all die-cuttingmachines. Always check with the printerbefore including them in the design.

Bar Coding To help keep bar codes pre-cise for lasers, they should be printed parallel to the direction of the web, andmust allow for dot gain.

Die-Cut Templates Templates can be exported from CAD systems to illustrationprograms, providing the designer with atwo dimensional layout of the job.

Staggering images on the plate can help keep continuous contact betweencylinders, minimizing platebounce. Sometimes it is necessary to place non-printing bearer bars onnon-image areas to main-tain contact.

19

Prep

ress

Out

putThe Prepress Process

Flexographic Imagesetting Requirements

Accuracy To optimize registra-tion, output devices should meeta minimum standard of �1 milover multiple separations. Geo-metric and absolute accuracycapabilities are also importantimagesetters considerations.

Size The imagesetter format sizeshould be large enough to makethe most effective and economicuse of film, given the particularapplication.

Film All film for soft photopoly-mer plates should be output tomatte emulsion film (minimumthickness: 0.004"; 0.007" is pre-ferred). This helps avoid trap-ping air between the film andplate during exposure.

Calibration Film dot percentagesbelow 10% should not vary bymore than 1%; areas over 10%should not vary by more than 3%.

Uniformity Screen tints shouldbe a uniform dot percentage,with no variation in size be-tween individual dots.

Dot Shape The imagesettershould be capable of outputtinga “hard” round dot.

Resolution Resolution should be between 1200 and 3600 dpi. For line art, solids and type,1200 dpi is adequate; halftonesrequire a minimum of 2400 dpi.

Density Film density is an important factor; imagesetterexposure levels and film pro-cessing chemistry should provide DMax areas of 3.5-4.0.

After a design has been trapped,distorted to compensate for plate elonga-tion, and electronically imposed (consid-ering step-and-repeat requirements), thefile is processed by the raster image

processor (RIP) and output to film orplate. The RIP converts PostScript

TMdata

into a series of bitmapped images. Thelaser output device records this visual information received from the RIP ontofilm or plate material. Larger, morecomplex files will take longer to processthrough the RIP than simple text files.

Following design, production, and ripping, a job may take different paths through the pre-press output and platemaking stages. For conventional photopolymer or rubber plates, jobsare first processed through an imagesetter, creating film output, which is used for plate exposure and processing. Plates are then placed on a mounting machine where, in somecases, a plate proof is made. A platesetter device essentially follows the same flow with theexception that the film processing step is eliminated. With direct-to-plate (or cylinder), de-vices, shown below as laser ablation, both platemaking and processing steps are eliminated.

20

Proo

fing Proofing for Flexography

Soft Proof

Digital Print Proof

Film Proofs

Plate Proof

Press Proof

In flexography, proofing forhalftone accuracy and colormatching can be difficult andinexact. A digital or film-based proof-ing method used in offset lithographymay not be suitable for different kindsof substrates, for matching spot colors,or for reproducing flexographic dot gain.Accurate proofing may require usingtwo or more methods.

Substrates

Most proofing methods are limited to a small number of substrates. Becauseink colors are affected by the absorptionand color of the substrate, proofing toanother material cannot provide accuratecolor matching.

Spot Colors

Since most film-based and digital proof-ing methods apply toner in CMYK colors, spot colors often cannot be accu-rately produced. If matching spot colorsis critical to a job, some printers canprovide a catalog of colors that they canconsistently print on a variety of sub-strates. Catalogs may contain speciallyformulated colors, or use systems similarto Pantone® or FocolTone

TM. Sometimes

it is possible to request samples. To ensure accurate matching, spot colorsshould also be evaluated by a color mea-surement instrument.

Dot Gain

Adjustments for flexographic dot gainare often not available in proofing sys-tems designed to mimic the dot gainfound in offset lithography. For this reason, halftone images and smaller type may not be accurately reproducedin the proof. However, once a character-ized profile is established for a givenpress using a color management system,dot gain can be simulated by a digitalproofing system.

During preliminary design, proofing starts with a monitor, some-times called a soft proof. A monitor can provide an overall view of the design, but RGB colors on a monitor will probably notmatch CMYK or spot colors printed on the substrate. Higher colorfidelity is possible by calibrating the monitor and by using a colormanagement system.

Flexographic printers often provide mock-up pack-ages, using proofs from digital laser printers.Many high-end digital proofing methods meet industry color standards for prepress proofingsystems. Inexpensive desktop color printers canalso give an approximation of specified colors.When used with a color management system, digital printers can provide contract proofs. Mostdigital systems are based on CMYK toner applica-tions, so spot colors may not be accurate.

Most film-based proofing systems are designed tocompensate for dot gain occurring in offset lithogra-phy. To use these systems for flexography, two sets of film must be printed. The first set, which is used for platemaking, reduces dots to compensate for theactual flexographic dot gain during printing. The sec-ond set, used for proofing, increases the dots to simu-late dot gain in the film proof.

For many years, flexographic printers haveused a plate proof created on a mounter-

proofer during plate mounting to verify plateregister, quality, and content. Though expen-sive and not intended for customer approval,the plate proof today is mostly used on wideweb presses. Plate proofs can be created forcolor matching, but they more commonly useink hues that are not intended to match presscolors. Color matching from a plate proof isvery difficult due to the differences betweenproofing and press equipment.

Printed on the press, a pressproof is the most accuratemethod, but because it is alsothe most expensive, it is notcommon.

What to Look For During a Press Check

Type Is the type sharp? Has the weight of the type changed? With a loupe, look for outline halos.

RegistrationAre the colors in register? Make sure colors line up and checkareas where inconsistent elongation may have caused mis-registration. For a four-color process with traditional screen-ing, color-to-color register should not vary by more than asingle row of halftone dots.

Density/Color IntensityIs the density of the color appropriate, especially in situationswhere screens and solids are printing from the same cylin-der? Is the color strength consistent from side to side?

Color MatchDo spot colors match? Each color should be verified under5000° Kelvin lighting conditions. When appropriate, use colormeasurement instruments to verify acceptable match.

Ink LaydownIs the ink laydown consistent, without mottle? Are there pinholes or voids? Under a loupe, halftone dots should appear sharp, not slurred.

SubstrateIs the width, caliper, and type of substrate as specified? If the substrate is an opaque film, is the opacity appropriate?

External RegisterDoes the print line-up with the specified finishing operation,such as diecuts, sideseals, slots, scores, and glue areas?Request a mock-up container to check accuracy of externalregister.

Ink and Impression LevelsLook at the edges of solids for an outline halo, which is theresult of excess ink or impression pressure. The press operator may be able to relieve some pressure; some platesmay have spot color inaccuracies that require a plate remake or remount.

Dot GainDot gain levels should be comparable to those achieved during fingerprint trial.

UPC and Bar Coding

Over-impression can change the width of bars and spaces,potentially making the bar code unreadable.

Wind Direction

Has the job been installed in the right direction on press? If the press is running roll-to-roll, is the print rewind in theproper direction?

Before a flexographic job isprinted, a number of factorsneed to be checked to ensure accuracy. Makeready on a flexographicpress includes installation of the requiredplate cylinders and inks, setting levels for impression and ink pressure, registeradjustment, and any setup for inline finishing, such as cutting, folding, orgluing. Pressure levels are particularlycritical for accurate printing. Finally,after press adjustments are complete, thepress operator checks colors for the job,running a sample at (or near) produc-tion speeds. Designers should also makesure to perform a press check for the firstactual print run.

These are some of the elements that

should be verified prior to printing.

Type

Is the point size and font correct? Is the typography what was expected? Has plateelongation affected leading, letterspacing,or word spacing?

Line Art

Have all of the images elongated and reproduced accurately?

Register

Internal (color to color) and external (images to die-cut, sealing areas, perfora-tions, etc.) If all colors have been accu-rately distorted, and the plates accuratelymounted, the job should be in register.

Traps

Have plate mounting and plate elongationmaintained accurate trap areas?

Bar Coding

Have the bar codes been positioned toallow proper open area surrounding thecode for scanning? Has the bar code beenpositioned with the bars parallel or per-pendicular to the web direction? Whenmounted perpendicular to the web direc-tion, bar codes will be affected by plateelongation.

Wind Direction

Has the job been set-up to print in theright direction on press? Will the print direction match the packaging or labelingoperation?

21

Prep

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22

Glo

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dex design roll: 2, 8

A rubber covered cylinder often used as animage carrier by flexographic printers. Reliefpatterns and images are created by ablatingthe surrounding non-image area with laserlight energy.

die-cutting: 18The process of using sharp steel rules to cutshapes for labels, boxes and containers, fromprinted sheets. Die-cutting can be done on either flat-bed or rotary presses. Rotary die-cutting is usually done inline with printing.

direct-to-plate: 8The process of using digital information tolaser image a printing plate or design roll, by-passing the film stage of production.

distortion: 9Intentional compensation for flexographicplate elongation.

distortion factor: 9A percentage number calculated by a plateelongation formula and applied to imagesprior to output of flexographic films.

dot gain: 15, 16An unavoidable increase in the size of half-tone dots as they pass through the stages ofplatemaking and printing. Dot gain varies according to the characteristics of the press,ink, and substrate used. If dot gain is not ac-counted for during the creating of color sepa-rations and proofs, unexpected color shifts orloss of detail will occur on press.

doctor blade: 4, 6A thin blade of metal or polyethylene mount-ed parallel to and in contact with an aniloxroll to meter excess ink from the non-cell areas.

dry trapping: 12The technique of printing multiple colors bydrying each color immediately after it is ap-plied and before the next ink is applied on orover it. Flexography and gravure print by drytrapping. See wet trapping

dual doctor ink chamber: 4, 6On a flexographic press, a cartridge designedto supply ink to the anilox roll in an enclosedarea. Ink is pumped into and circulatedthrough the cartridge which is positioned onthe anilox roll. Two thin strips of metal orpolyethylene (doctor blades) are in directcontact with the anilox roll. One of theblades contains the ink within the cartridge,the other blade contains and meters the inkfrom the non-cell areas of the anilox. Whenusing a dual doctor ink chamber, the foun-tain roll can be eliminated.

ablating: 8To remove by cutting, erosion, evaporation,or vaporization. In flexography, laser ablatingis used to image design rolls and plates.

anilox: 5, 6, 17An engraved metal or ceramic roll used tometer ink in the flexographic inking system.

bearer bars: 18Continuous strips of plate material usuallyplaced on the outside of printing areas tominimize plate bounce and over-impressionby taking up excess impression pressure dur-ing printing operations.

blanket: 4In offset printing, a rubber-surfaced fabricwhich is clamped around a cylinder, to whichthe image is transferred from the plate, andfrom which it is transferred to the paper.

bleeds: 18An image or color that extends to, and slightlybeyond, the trimmed edge of a printed piece.

calendered paper: 10Paper that has been passed through a group ofrolls to reduce thickness, increase density, andimprove its surface smoothness and gloss.

caliper: 10Thickness of a substrate, usually measured inthousandths of an inch.

cell angle: 6, 17On an anilox roll, the measure of a linedrawn through the center of a row of cellsand a line drawn parallel to the shaft of theanilox. The angle at which cells are arrangedon an anilox roll.

cells per inch (CPI): 4, 17On an anilox roll, the number of cells in alinear inch.

cell volume: 6A measure of the capacity to carry ink of asquare inch of anilox roll. Cell volume maybe calculated as theoretical volume, or mea-sured by a technique of liquid volume mea-surement, or scientifically measured by atechnique known as infratometry.

choke: 12A trapping technique of slightly reducing thesize of a line, an image element, or a dot tocreate a trap.

clay coated: 10 A high-quality paperboard having a surfacecoating of pigment or pigment like solids andappropriate binders.

colorimeter: 14Any of various instruments used to determineor specify colors. A colorimeter measures thespectral reflectance of a color, and computesnumeric values for the hue, intensity, and purity.

color management system (CMS): 14A software system used to ensure color con-sistency among different input and outputdevices so that printed results match originals.

common impression cylinder press (CIC):

6, 7A printing press configuration that positionsall color decks around a central impressioncylinder. The CIC press configuration offersweb support throughout the printing opera-tions, and optimum registration capabilities.

computer aided design (CAD): 18Electronic equipment used by package designengineers to layout and design in threedimensions the structure of a package.

continuous repeat: 7The ability to print patterns or images on aweb of substrate, void of any gaps in theprinting.

contract proof: 20A proof supplied to a printer to documentthe color results expected on the press.

converting operations: 7In packaging, any process performed to man-ufacture a completed package from a raw material or an unfinished material.

corrugated: 6, 7, 10The combination of linerboard and corrugat-ing medium as a fluted material.

corrugated press: 2, 7An inline sheet-fed press (usually a flexo-graphic press) designed for printing sheets of corrugated.

cut areas: 18In die-cutting, a region of a package that willbe cut-out as a window or as part of thepackage construction, or as a slot for a clo-sure tab.

cylinder: 5In flexography, the term cylinder usuallyrefers to the rollers on which plates aremounted (plate cylinders), and the impres-sion roller (impression cylinder).

Glo

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23

durometer: 15A measure of the hardness of rubber. Themeasuring instrument most widely used is a “Shore A” durometer gauge.

fingerprint: 12, 14, 15A method of testing characteristics of a print-ing press by use of a test plate.

fluted material

A paper substrate formed into rounded pleatsand sandwiched between two paper liner-boards. Fluting material adds structuralstrength to corrugated board.

fountain roll: 6In flexography, a rubber covered roll in thetwo roll flexographic inking system. The func-tion of the fountain roll in a two roll systemis to deliver and meter ink to the anilox roll.

fountain solution: 4In lithography, a solution of water, a naturalor synthetic gum, and other chemicals used to dampen the plate and keep non-printingareas from accepting ink.

freesheet paper: 10Paper free of mechanical wood pulp.

gradation: 14A smooth transition between shades.

gravure: 2, 4An intaglio printing process that uses an engraved plate as a master image carrier.Gravure is used for printing packaging, speciality products, and publications.

HiFi, high fidelity: 11, 17A method of increasing the process colorprinting gamut by printing six, and some-times seven, process colors.

image carrier: 4The physical component of a printing pressresponsible for transferring ink from the inkdistribution system to the appropriate areasof a substrate.

impression cylinder: 4, 6The cylinder that provides web support dur-ing image transfer from plate to substrate.

inline finishing: 7Any converting operation done as a con-tinuous process with a printing operation, including lamination, die-cutting, perforat-ing, folding, and sealing.

inline press: 6, 7A multicolor press where the printing unitsare assembled on a common plane, or inlinewith one another. Also refers to any combi-nation of printing and converting operationdone simultaneously.

intaglio: 4A process in which the image is recessedbelow the non-image area, used in gravureand steel die engraving.

kraft linerboard: 10A type of paper made from chemicallypulped wood fibers, and used as the top and bottom layers in a sheet of corrugated.

kiss: 6In flexographic printing, the lightest contactpressure necessary for complete image trans-fer to a substrate.

laser ablation: 8A process of imaging onto rubber or pho-topolymer design rolls or plates. Images arecreated by ablating the surrounding non-image area with laser light energy.

lithography: 2, 4A method of printing from a plane surface(such as a smooth stone or metal plate) onwhich the image to be printed is ink-recep-tive and the nonprinting area ink repellent.

lpi: 5,16, 17(lines per inch) A measure of the frequencyof a halftone screen, usually ranging from 55-300. Originally, halftones were made byplacing an etched glass plate over an image andexposing it to produce dots. Lpi refers to thefrequency of the horizontal and vertical lines.

metallized film, metallized paper: 10Paper or film that has been “coated” with amicroscopic film of metal. A metallized paperor film is produced by melting and vaporiz-ing aluminum in a vacuum while passing aweb of paper around a chilled roller and over the point of vaporization. Vaporizedmolecules collect on the cool web, giving thepaper or film a metallic finish.

moiré: 6, 17A repetitive interference pattern caused byoverlapping symmetrical grids of dots or lineshaving a differing pitch or angle.

mounting tape: 9A compressible, or a non-compressible sub-strate with adhesive applied to both sides,and used for affixing flexographic printingplates to plate cylinders. Mounting tapes areavailable in a variety of types and thicknesses.

nailhead: 12In flexographic printing, an ink drying prob-lem usually caused by two or more colorsprinted on top of one another in a trappingsituation, resulting in incomplete drying tothe successive ink layers, and an ink pick-offarea that resembles the head of a nail.

narrow web: 6The limit of narrow web flexography hasbeen specified to be as narrow as 18" or aswide as 32" by various sources within the in-dustry. There is presently no agreement onthe exact cut-off width that differentiateswide web from narrow web.

nesting: 7, 18A technique of placing images between otherimages on a flexographic step-and-repeat layout. Nesting is done to minimize substratewaste, and/or to minimize flexographic platebounce.

nip: 6Contact point between two rollers, usually ametal driven roller and undriven rubber cov-ered roller.

offset lithography: 4Planographic print using an intermediateblanket cylinder to transfer an image fromthe lithographic plate to the substrate.

over-impression: 13, 15In a flexographic press set-up, excess pressurebetween the plate and the impression roll.

paperboard: 10There is some question as to the distinctionbetween paper and paperboard. Paperboardis thicker, heavier in basis weight, and morerigid than paper. Most paper that is over 12points (0.012") thick is considered paper-board, however, some thinner papers with athickness of 10 points (0.010") are also con-sidered to be paperboard.

photopolymer: 8Any of a variety of materials that undergo achemical change when exposed to ultravioletlight.

planographic: 4A process for printing from a plane surface,both image and non-image are carried on acommon plane as in lithography.

plate elongation: 9In flexographic printing, a physical lengthen-ing of the flexographic image carrier aroundthe cylinder or curve direction, that occursduring the plate mounting step.

24

Glo

ssary

& In

dex plate bounce: 18

An erratic rotation of a printing press cylin-der, such as a plate cylinder, that results indefective impressions. This is caused by thelead edge of image areas on a flexographicplate cylinder coming in contact with theanilox or impression roll.

plate proofs: 20A print made from the “live” productionplates prior to going to press. Plate proofs areusually not appropriate for evaluating colorresults, but may be used as an in-house quali-ty control proof before going to press.

plate thickness: 9A measure of the height of a flexographicplate from the back to the top of the imagearea, usually expressed in thousandths of aninch.

polyethylene films: 2, 5, 10Thin clear substrates used as packaging materials, commonly known as plastic as inplastic bags.

polymer films: 10Any one of a number of different non-absorbent, thin, clear, or colored substrates used as packaging materials, and commonlyreferred to as plastics.

printing plate: 4In flexography, a rubber or photopolymermaterial used as the image carrier to transferink from anilox to substrate.

proof, proofing: 20A prototype of a job to be printed that ismade from plates, film or electronic data.Used for in-house quality control and/or forcustomer inspection and approval.

raster image processor (RIP): 19The computerized process that results in anelectronic bitmap which indicates every spotposition on a page in preparation for actualprintout.

reflection densitometer: 14An apparatus for measuring the optical densi-ty, or light absorbing qualities, of an ink.

relief: 5In printing, a process that prints from raisedimage areas.

repeat length: 7Printing length of a plate cylinder determinedby one revolution of the plate cylinder gear.

resolution: 16, 17The measure of fineness and detail in animage. The scale of resolution depends onthe device being measured. Scans are mea-sured in samples per inch (spi) or pixels perinch (ppi). Monitors are measured in ppi.Halftone screens can be measured in lines perinch (lpi). In all cases, the higher the resolu-tion, the more detailed the image.

reverse side printing: 11Printing the underside of a clear substrate.Sometimes called back printing.

run-length: 5The size of a printing job, usually indicatedby the number of impressions or footage re-quired to complete the job. Also, the numberof impressions that may be expected from aprinting plate or a set of printing plates.

solid bleached sulfate: 10Paperboard made with sulfate pulp contain-ing 100% bleached fibers.

spectrophotometer: 14An instrument used to determine the distri-bution of light energy reflected by a color ora printed ink.

spot color: 11Color printed with a custom ink, rather thanwith a process color combination.

spread: 12A prepress function that compensates forprinting press misregistration. A spread is theslight size increase of the inserted image.

stack press: 7A multicolor printing press where all colorunits are built vertically or stacked.

step-and-repeat: 18In photomechanics, imagesetting, or plate ex-posure, the procedure of multiple exposuresusing the same image information by step-ping it in position according to a predeter-mined layout.

stochastic screening: 17Also called frequency modulated or FMscreening. An alternative to conventionalscreening that separates an image into veryfine, randomly placed microdots, rather thana grid of geometrically aligned halftone cells.

substrate: 4, 10A material on which print or coating is applied, such as paper, polyethylene, or foil.

trap, trapping: 12In prepress, a technique which allows forvariation in registration during the press run.On the desktop, this is done primarily by al-lowing an overlap between abutting colors.

variable repeat length: 7In printing, the capability of a printing pressto print from various size plate cylinders orprinting plates.

vignettes: 16An image in which the background fadesgradually away until it blends into the unprinted substrate.

wet-out: 10The tendency of an ink to level-out as woulda true liquid. On a substrate, an ink filmshould flow and level itself rather than beading.

wet trapping: 12The technique of printing multiple colorswhereby each succeeding ink film remainsopen (not dry) as the next color is applied on or over it.

white back-up plate: 11A printing plate made for applying a solidwhite ink as a reflective base under all coloredimages on a clear substrate.

wide web: 6The lower limit of wide web flexo has beenspecified to be as narrow as 18" or as wide as32" by various sources within the flexograph-ic industry. There is presently no agreementon the exact cut-off width that differentiateswide web from narrow web.

windows: 18In packaging, an area of a package that willbe cut out (or left clear on clear substrates) toexpose the product held within the package.

Working With Prepress and Printing SuppliersDigital Color Prepress - Volume Three

This booklet explains key elements in the relationship between document creators andtheir service providers. Contains time-savingtips to ensure successful transition of jobsfrom design to film output to final print.

An Introduction to Digital ScanningDigital Color Prepress - Volume Four

This booklet focuses specifically on many key aspects of scanning. Contains 40 pages of both basic and advanced information, presented objectively and graphically. An essential reference for scanner users with any level of expertise.

The Agfa Guide to Digital Color PrepressMacintosh CD-ROM Edition

The ultimate companion to the award-winning Digital Color Prepress series. This CD-ROM contains over 630 Mb of interactive content, including 350 screens of detailed information, numerous anima-tions, videos, voiceovers, glossary, timeline, build-a-page game, and more.

A Guide to Digital PhotographyTheory and Basics

This all-new guide is a must read for any-one working with or interested in digitalphotography. Offers clear, visual explana-tions on traditional photography basics aswell as key concepts from the emergingdigital realm.

PostScript Process Color Guide—1996 EditionThis 52-page oversized reference containsover 17,000 electronically created CMY andCMY+K process color combinations (oncoated and uncoated stock), intended to helppredict how colors on the screen will look in print. Also includes production tips, instructions for use, and special color viewingtemplates. Available in U.S. (SWOP) and amultilingual European standard version.

Other Educational and Reference Materials from Agfa

For more information or to order,

see contact listings on back cover.

An Introduction to Digital Photo ImagingThis booklet looks at how computer technol-ogy is blending with and changing traditionalphotography, and the impact it has on photog-raphers and imaging professionals. Explainshow to evaluate digital cameras, scanners,input and output devices, and how to get started in this emerging field.

A Guide to Color Separation Digital Color Prepress - Volume Two

This booklet provides a more advanced look at the topic of PostScript color. A special emphasis is placed on reproducing color pagesin print, including the use of HiFi color andstochastic screening.

An Introduction to Digital Color PrintingA first-ever publication that provides an objec-tive look at technology, applications, and processes. Learn how to save time and moneyand use digital printing to your best advantage.Includes a bound-in digitally printed insertfor comparison with offset printing.

An Introduction to Digital Color Prepress—1997 EditionA fundamental reference for anyone interest-ed in PostScript color. Basic concepts are ex-plained in a clear, objective and highly visualway. A useful and award-winning volume,with over 400,000 copies in print in eightlanguages.

Credits

Writing and Technical Direction:Barry LeeRochester Institute of Technology, Rochester, NY

Creative Direction and Design:Lynne Stiles and Maria GiudiceYO, San Francisco, CA

Copyediting:Robert ShusterSeattle, WA

Illustrations:Steve McGuireMcGuire Design, Martinez, CA

Special Thanks:Don Haaga, Ben Seibel

This publication copyright ©1997by Bayer Corp. All rights reserved.

No portion of this publication may be reproduced in any form without expressedwritten permission from the publisher.

NEEJ1First PrintingMay 1997Printed in Belgium by The Color Revolution

Agfa Educational PublishingP.O. Box 787Randolph, MA 02368-0787 USAPhone: 1-800-395-7007Fax: 1-617-341-6261http://www.agfahome.com

Production Notes

This booklet was produced using a variety of Macintosh computers. The illustrationswere created using Adobe Illustrator andAdobe Photoshop. All images and text wereimported into QuarkXPress for page layout.Pages were individually output to the AgfaSelectSet 5000 imagesetter using AgfaBalanced Screening. Printing was done infour-color process plus one spot color, PMS407, on Centura Dull Coated 80# book stock.

Film Preparation:Digital Pre-Press InternationalSan Francisco, CA

Printing Supervision:Jack GaidoHemlock Printers, Burlingame, CA

Printing: Hemlock PrintersVancouver, Canada

Ordering Information:This booklet is part of a series of educationaland reference materials published by Agfa. If you’d like to be on our mailing list, or obtain information about other publications in the Digital Color Prepress series, contactus via the numbers or addresses below.Quantity discounts and foreign languageversions available.

Agfa Educational PublishingP.O. Box 200Stephenson Road – GroundwellSwindon, Wilts SN2 5AN UKPhone: 0793-707099Fax: 0793-705745

AGFA, the Agfa rhombus, ColorTune, and Digital Color Prepress are trademarks of Agfa-GevaertAG. Macintosh is a registered trademark of Apple Computer Inc. PostScript, Photoshop andIllustrator are trademarks of Adobe Systems Inc. and may be registered in certain jurisdictions.QuarkXPress is a registered trademark of Quark Inc. Pantone and PMS are registered trademarksof Pantone, Inc., for color reproduction and color reproduction materials. FreeHand is a trademarkof Macromedia, Inc. Windows is a trademark of Microsoft Corporation. FocolTone is a trademarkof FocolTone USA Inc. Trapwise is a trademark of Luminous Corporation. DK&A Island Trapper isa trademark of DK&A Inc. All trademarks have been used in an editorial context with no intentionof infringement.