flexo and packaging

7/28/2019 Flexo and Packaging

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Look around youon store shelves, in your homeand yourecertain to see material thats 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 someof the most important advertising for the products themselves.Flexographys soft compressible plates, fast-drying inks, and itssimple, 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 rateunparalleled by any other printing technology. Although someof this growth can be attributed to a greater need for packaging,flexography is increasingly used in markets traditionally served by

gravure and offset lithography. Since advances in technology havesignificantly improved flexographys ability to print accurate type,color, and halftone images, manufacturers and print buyers arerecognizing flexography as a high-quality, economical alternativeto 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, servicebureaus, and printers.


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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 redthroughout this guide can

also be found in the glossary.


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Flexogra

phicMarkets

2

The use of flexography is grow-ing in popularity in todaysprinting markets, where shortrun, low-cost, and high-qualityare crucial to success.A look atthe development of flexography reveals

a printing technology and culture that

has been willing and capable of changein response to the needs of the packag-

ing industry. An evolutionary process

of improvements in materials and

equipment, rather than a single discov-

ery, has led to flexography as it is

known today.

The first use of soft compressible plates

can be traced back to the late 1880s,

when letterpress printers needed to find

a way to print kraft paper grocery bagsand corrugated boxes. The materials

were rough in texture, and did not

respond well to the ink transfer pressure

of hard letterpress plates. To solve the

problem, printers began creating plates

from rubber, rather than from wood or

lead. This quickly became the dominant

method for printing corrugated, and

also 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 period

for flexography.

Clear Packaging

In the early-to-mid 1920s, flexographic

printers responded quickly to the intro-

duction of cellophane as a clear packag-

ing material. White inks were developed,

drying systems were improved for cello-

phanes non-absorbent surface, and presstension systems were refined to handle

its caliper and weight. Approximately

ten years later, polyethylenewas intro-

duced, and went on to become the most

commonly 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 impression

pressure make flexography well suited for

printing 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-absorbent

polymer film, including bread bags, snack

food bags, candy wrappers, pouches, and

textile wrap.

Gift Wrap and Wallpaper

A continuous repeat allows the printing of

products such as wallpaper and gift wrap.

Design rolls, which do not have a plate

seam, are used to print a continuous back-

ground color.

Envelopes

Flexography is used to print many kinds

of envelopes, including those for direct

mail, sweepstakes, general mailing, and

overnight delivery. The security printing

on the inside of many envelopes is often

applied by flexography.

Folding Cartons

Although folding cartons, including cereal,

detergent, and cosmetic boxes, are printed

by both the lithographic and gravure pro-cesses, flexography has recently increased

its market share due to improved quality.

Rigid Paper Boxes

Rigid paper boxes, or pre-formed boxes

are used for bakery products, shoes, and

neckties.


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Origins of the Name

Originally, flexography was known

as aniline printing, a name taken from

the aniline dyes used as colorants for

the ink. Aniline dyes, however, were

considered toxic and eventually banned

for use on food packaging. New inks

were developed as replacements, butthe name remained until 1951, when

Franklin Moss, a leader in package

printing, started a campaign to change

it. He asked aniline printers and suppliers

for suggestions, receiving over two

hundred. Of those, three finalists were

selected: permatone process, rotopake

process, and flexography. After a vote,

the process came to be known as flexog-

raphy in 1952.

In the United States, the Clean Air Act

of 1980 began a development in flexog-

raphy toward environmentally friendly

printing using low-solvent and no-solvent

inks. Today, flexography is often chosen

because of the ability to print with clean

water based or solventless ultraviolet inks.

Today the process continues to adapt.

As the technology is refined, quality

continues to increase, making flexogra-phy the leader in packaging graphics

applications.

Paper Grocery Bags

The paper bag is the original flexographic

product. In the late 1800s flexography

evolved from the need to apply graphics

to plain brown grocery sacks. The evolution

continues today.

Plastic Carrier Bags

Flexography can add advertising and

graphics to plastic bags that are carried

by customers in stores.

Milk CartonsApproximately 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 the

entire 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 immediately

after printing. The quality of many flexo-

graphic labels is equal to or better than

that offered by lithography or gravure.

Pre-printed Linerboard

Pre-printing linerboard allows high-quality

graphics to be placed on corrugated containers.


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TraditionalPrintingProcesses

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 print

magazines, catalogs, and daily newspa-

pers, as well as annual reports, advertising,

and art reproduction. Offset lithography

can also print paper-based packaging,

such as cartons, labels, and bags.

Offset lithography is aplanographicprocess, meaning that the printing plate

holds both the image and non-image

areas on one flat surface or plane. On

most offset presses, image areas on the

plate are chemically treated to attract the

lithographic paste ink, while afountain

solution or ink repellent chemical

treatment protects non-image areas from

inking. From the plate, the image is first

transferred to ablanket (hence the term

offset), and then to the paper or othermaterial, known as the substrate. To

dry, most lithographic inks require a

certain period of time or an application

of heat.

Gravure

The gravure method, sometimes known

as 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 the

third in the United States. Gravure is

used to print high-volume products

such as packaging, magazines and the

advertising inserts found in newspapers.

In addition, offset versions of gravure

presses are used to print labels or logos


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Traditional Printing Processes

Magazines,

newspapers,

advertising pieces,annual reports, cereal

boxes, bags, tags &

labels

Coated & uncoated

papers, newsprint,

some polymer

packaging films

Moderate to heavy

300,000 to 400,000

maximum

impressions

Sheet-fed: to 60"

Web: 11" to 60"

Standard format with

limited repeat length

Product dependent:Magazines: 2,500 fpm

Sheet fed: 12,000

impressions per hour

Paste ink

Oil & soy based

Heat set & non-heat set

Wet trapping

65-300 lpi

Most common:

133-150 lpi

3-5%

Midtones: 20%

Magazines &

catalogs, Sunday

supplements, candywrappers, cereal

boxes, snack food

bags, vinyl flooring

Coated & uncoated

papers, newsprint,

paperboard, foil,

metallized paper,

polyethylene vinyl,

polypropylene,

cellophane,

polystyrene

Heavy

6 to 7 million

impressions average;

longer with

rechromed cylinder

2" to 144"

Infinitely variable

repeat length

Product dependent:Magazines: 3,000 fpm

Bread bags: 500-900

fpm

Vinyl flooring: 50 fpm

Fast drying fluid ink

Solvent & water-based

Dry trapping

120-300 lpi

Most common:

150 lpi

3%

Midtones: 23-26%

Newspapers,

phone directories,

corrugatedcontainers, 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 corrugated

presses

Variable repeat length

Product dependent:Toilet tissue: 3,000 fpm

Bread bags: 500-900 fpm

Pressure sensitive

labels: 100-300 fpm

Fast drying fluid ink

Solvent & water-based

UV curable

Dry trapping

45-150 lpi

Most common:

100-133 lpi

8-12%

Midtones: 20-25%

Typical

Uses

Substrates

ImpressionPressure

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 on

M&M candy.

Gravure is an intaglio process, in which

the image area is recessed below the

level of the non-image areas. The image

is etched or engraved in a cell format

onto a copper plate or copper-platedcylinder. By varying the size and depth

of each cell, a printer using a gravure

press can vary tones. Often, after the

copper is etched or engraved, the plate

or cylinder is plated with chrome to add

durability and increase its run-length.

A fast drying ink fills the recessed cells,

a thin metal strip called adoctor blade

clears the non-image area of ink, and

the image is transferred directly to the

substrate 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 packaging

materials, such as corrugated and paper-

board. The fast-drying fluid inks used

in flexography are ideal for such materi-

als as polyethylene films, used for plastic

grocery bags. Flexographic presses areoften part of a manufacturing process,

in which packaging is printed, folded,

shaped, and die-cut.

Flexography is characterized as arelief

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 plate

is then moved into light contact withthe substrate to transfer the image. The

minimal pressure during image transfer

allows printing on material, such as cor-

rugated board, that may be adversely

affected by impression pressure.


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6

FlexographicTechnology 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 CPI

increases, 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 the

printing plate and the cell angle can combine to cause a moir pattern, even

with one color halftones. Moir 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 adoctor blade, and the dual

doctor ink chamber system.

Two roll units are usually found on older

flexographic presses, and on narrowweb presses. Narrow web presses

equipped for process colors often use

the two roll unit with a doctor blade,

and more modern wide web presses

use the dual doctor ink chamber system.

Each type of flexographic press uses an

anilox roll. The surface of every anilox

roll is engraved with a pattern of tiny

cells, so small they can only be seen

under magnification. The size andnumber of these cells determine how

much ink will be delivered to the image

areas of the plate, and ultimately to the

substrate. An anilox roll is either copper

engraved and then chrome-plated, or

ceramic coated steel with a laser engraved

cell surface.

Anilox rolls are carefully selected for

specific types of printing, substrates,

and customer requirements. Often theflexographic printer will perform test

runs to determine the ideal anilox for

producing the desired ink distribution

for halftones, spot color, and solids.

The design of the flexographic printing

unit enables press manufacturers to

build presses in any one of three config-

urations: the stack press, the inline

press (includingcorrugated presses),

and the common impression cylinderpress. Each configuration can be

equipped with any of the basic printing

units, depending upon the needs of the

flexographic printer.

On a two-roll flexographic printing unit,

the rubber covered fountain roll rotates

in a fluid ink bath, dragging ink from the

pan to cells of the anilox roll. The soft

rubber 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-cell

areas. Once past the nip point, each cell

is filled with ink, and a measured, repeat-

able amount of ink is available to the

printing plate. The metered anilox roll

is moved into light kiss contact with the

image areas of the plate, and the plate

cylinder is moved into kiss contact with

the substrate to transfer the image. The

steel impression cylinder supports the

substrate. When a thin metal or poly-

ethylene doctor blade is used with a

two-roll unit, the nip point between the

fountain and the anilox roll is opened to

allow ink to flood the anilox and fill the

cells. The doctor blade comes into con-tact with the anilox to clear excess ink

from non-cell areas. With a dual doctor

ink chamber, the fountain roll and inking

pan can be eliminated; ink is delivered

directly to the anilox through an enclosed

chamber.


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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 diameters

can be mounted on many flexographic

presses, allowing for variable repeat

lengths. Printing a roll of packaging, such

as gift wrap, uses a continuous repeat,

where the same set of images is repeated

many times on a continuous stream of

substrate. To avoid the plate seam, images

may require nesting, an arrangement that

creates a staggered effect. Staggering im-

ages gives the appearance that the design

is continuous, no matter where the sub-

strate is cut.


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FlexographicPlates

8

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 processingphotopoly-

mer, and imaging with lasers. While

molded rubber plates have been used

since the 1930s, photopolymer plates,

introduced in the 1970s, generally pro-vide higher resolution and more accu-

rate color registration. Direct-to-plate

laser imaging, called ablating, is avail-

able for both materials. Selection of a

particular type of plate depends on the

press, the plate cylinder inventory, and

the customers requirements, such as

resolution, registration, and cost.

Molded Rubber

Molded rubber plates are created in amultistep process that involves exposing

and etching a magnesium plate, making

a mold, and then placing the image on

the rubber plate using a molding press.

Photopolymer

Light-sensitive photopolymer is supplied

in either solid sheets or in a thick liquid

state. The image area of the plate is

exposed through a film negative. Liquid

photopolymer, about the consistencyof 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 computer

to the plate, a process known as direct-

to-plate that avoids the production of

film. Some photopolymer plates can be

directly imaged by lasers and then con-ventionally processed. Adesign roll is

a cylinder covered with rubber or photo-

polymer and molded or imaged by a

laser. Design rolls can provide a true

continuous repeat with a continuous

background color. Laser ablated plates

must be nested to hide the plate seam

for the appearance of continuous repeat.

Molded rubber plates shrink when they

are removed from the molding press.

Plate films should be adjusted to com-

pensate for shrinkage, which is typically

1.5%-2.0% in the direction of the rubber

grain, and .5%-1% across it. Exactshrinkage amounts should be commu-

nicated between production artists and

platemakers.

Line screening is limited to 120 lpi.

Registration can be more difficult than

with photopolymer plates.

Nesting is required for the appearance

of continuous repeat.

It is difficult to mold accurate rubber

plates larger than 24" X 36". Larger

designs must be placed on multiple

plates for each color.

Line screening is at least 150 lpi and can

be as high as 200 lpi.

Nesting is required for the appearance

of continuous repeat.

Positioning and register devices on

most modern flexographic presses are

designed for one-piece photopolymer

plates.

Direct-to-plate laser imaging is available.

Line screening is limited to 100 lpi for

tone reproduction, but can be 200 -300

lpi 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


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Plate Elongation

Distortion

Expected result

Plate elongationoccurs aroundthe cylinder

Printed piece with-out compensationfor 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 thecylinder or curve direction, the images willincrease 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 plateelongation. Film is output to 11.491" (12" 5.09")

or 95.7% in the curve direction, and 100% in thenon-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 elongationhas been compensated for.

11.491"

12"

When designing images forflexographic printing, it isimportant to understand theeffects ofplate elongation. Becauseflexographic plates are made with soft

material, they tend to stretch when

mounted on the plate cylinder, some-

times distorting images and text. A cir-cle, for example, may be stretched to

look more like an oval.

Fortunately, special flexographic soft-

ware can compensate for plate elonga-

tion by slightly distorting images.

Distortion is usually performed within

the 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 fasten

it, and on the circumference of the

cylinder (the repeat length). In general,

thicker plates and shorter repeat lengths

increase the elongation.

To be sure that images will be printed

with the correct size and shape, the

design should be output to film after

plate 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 the

need 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 a

curved surface, no stretching occurs.

As the soft plate wraps around the cylinder, it can

elongate, stretching images, halftones, and text across

the curve dimension. Without compensation for plate

elongation, images will not print as designed. In the

example, if no compensation is applied, the sun image

is printed as an oval and the vertical lines on each side

are lengthened.

Special flexographic software can compensate for plate elongation by adding distortion,

using a basic formula, as shown in the following example.


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10

Substrates

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, candy

wrappers, 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

Color

Dependent 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 light

to pass through.

SmoothnessSmoother substrates allow higher lpi; rough,

irregular surfaces require much lower lpi.

AbsorptionDetermines how ink dries and spreads. Low

absorption produces drying at the surface,

increasing color saturation and decreasing

dot 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-gloss

finishes.

CaliperThickness of a substrate, as measured by a

micrometer.

White, brown kraft, a varietyof colored papers.

Increases with bleached &

coated papers. Decreases

with greater amounts of re-

cycled fiber. Optical bright-

eners can be added.

Thin, lightweight papers

have lower opacity & are

more likely to have ink show

through.

Newsprint, corrugated liner-

board & paperboard are rela-

tively rough; calendered &

coated papers smoothest.

Newsprint, corrugated liner-

board & paperboard are very

absorbent, calendered; coat-

ed papers are less absorbent

& exhibit high ink hold-out.

Calendered & coated papers

are high gloss; corrugatedlinerboard, newsprint &

paperboard are low gloss.

Range: .002" to .010";

paperboard .010". Thin

papers more consistent in

caliper; paperboard more

inconsistent.

Clear, white or colored.

Determined by the opacity

of white film. Clear films

require the use of a white

plate.

Low for thin, lightweight

papers, which are more

likely to let ink show through

on reverse side.

Smooth printing surfaces;

ink adhesion is sometimes

a problem.

Non-absorbent, with no dot

gain.

High for most films, but

films can be produced witha matte finish.

Ranges from .00065" to

.006". Thin films may stretch;

inconsistency in caliper can

cause misregistration and

wrinkling.

Determined by the top-mostlayer.

Determined by the top most

layer. Foil & metallized sur-

faces require the use of a

white plate.

Higher with multiple layers

of material.

Determined by the top-most

layer.

Usually low, but determined

by the substrate used as a

printing surface.

Determined by the top-most

layer.

Increases as layers are

added. Thin layers may be

laminated together to ob-

tain the required thickness.

Flexography is ideal for printingpackaging materials because thesoft plates can transfer ink to manydifferent kinds of substratesanything

from corrugated board to candy wrap-

pers. The quality of a printed product

is determined not only by the type of

plate, but also by the substrate itself.Different substrates allow varying degrees

of ink absorption, gloss, brightness, and

color definition. The chart on this page

lists the characteristics of some common

substrates.


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White Plate

Multicolor Options

Reverse-Side Printing

In flexography, opaque spot colors are

printed 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 reflective

background that improves the color intensity. The

colored inks are then printed on top of the white

background.

An exception to the rule of light-

est to darkest printing occurs

when a spot color or line art

job calls for reverse-side print-

ing, sometimes called back

printing. Styrofoam products

are often decorated by laminat-

ing a reverse-side printed film.

Some snack food packaging is

also done this way.

Because the appeal of packagingis significantly enhanced bycolor, flexographic presses com-monly offer six and eight colors, and

even as many as twelve for limited

applications. Designers can choose from

a number of different combinations,

including multiple spot colors and HiFiprinting, which is a method of increas-

ing the color gamut by printing six or

seven process colors.

Most flexographic inks consist of

opaque or semi-opaque pigments. To

ensure proper ink coverage, the spot

colors are usually printed from lightest

to darkest. Process color inks are made

from transparent pigments and can be

applied in any sequence. Transparentsubstrates, such as polypropylene, require

awhite backup plate provided by a

choke plate, as a background for col-

ors; otherwise, colors would appear flat

and translucent.

Another technique used for applying ink

to transparent substrates is reverse-side

printing. The image is laterally reversed,

and colors are printed instead from

darkest to lightest; the packaging is thendisplayed from the non-ink side of the

substrate. This provides a scratch proof

surface to the ink layer, and a glossy fin-

ish. In some cases, a water-based ink is

used for reverse-side printing lamina-

tion. Paper or styrofoam plates are often

decorated by laminating a reverse-side

printed film layer to the plate.

Corrugated containers have historically

been only one color on brown kraftpaper linerboard, but more designers are

taking advantage of multiple spot and

four-color process capabilities. In some

cases, printing is done directly on a white

or clay coated corrugated linerboard,

avoiding the costly practice of applying

labels to achieve high quality graphics.


14/28

Trap affecting colors

Nailheads

12

Trapping

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 of

color, called misregistration, can be

caused by substrate handling and ten-

sion problems on the press, irregular

plate elongation from one color to thenext, inaccuracies in plate mounting,

plate bounce, and limited register capa-

bilities, especially with molded rubber

plates. A test run, called afingerprint-

ing analysis, can determine the registra-

tion tolerances.

When designing packaging for flexo-

graphic printing, it is best to avoid the

requirement for tight registration, to

design images with dominant colorsprinted on top of lighter ones, and to

avoid 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 the

help of service bureaus and special

trapping software programs, such as

TrapwiseTM from Luminous Corporation

or DK&A Island TrapperTM.

Trap widths on narrow web presses

should 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 if

an 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 of

1/64" 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 is

spread into the darker color, slightly increasing the size of the graphic element. When a

darker element appears against a lighter background, the knockout is choked by slightly

filling it with the lighter color. Both methods create a small overlap of ink colors, called

the 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 be

spread 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.


15/28

Typographic Guidelines

Type Weight

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: FILTER

AR, CORN SYRUP

A AND LOWFAT

CESSED WITH AL

IN, NATURAL VA

EDIENTS: FILTER

AR, CORN SYRUP

A AND LOWFAT

CESSED WITH AL

IN, 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, the

soft plate compresses

in the printing nip,

causing the fluid ink

to flow slightly out-

ward from the image

area. Thus the weight

of type may appear toincrease, and reverse

type may fill-in.

Made in the U.S.A.

47c94m15y

5k

47c94m15y5k

Letterspacing and/or linespacing may

increase slightly from plate elongation.

Avoid placing fine type on the same color plate

with line work and solid printing areas.

Avoid reversing type out of two or more colors

unless 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, tends

to get filled in.

To help compensate for the typographic

weight gain, it is possible to use the

trapping techniques of spreading on

positive type and choking on reverse

type. Software programs, such as

MacroMedia FreeHandTM and Adobe

IllustratorTM

, let the designer adjust thethickness of type. Some compensation

can be done by choosing either a lighter

or bolder face. For example, if medium

positive type is desired, use a lighter

weight face; if a medium reverse type is

desired, specify a bold face. When possi-

ble, sans-serif fonts should be used. In

general, larger point sizes produce more

consistent type.

Letterspacing must also be considered.Letters squeezed together for a denser

appearance with offset lithography may

merge together unacceptably in flexog-

raphy. Ideal letterspacing keeps letters

close enough together so that they lend

support to each other while under the

pressure of the printing nip, but sepa-

rated enough to avoid merging.


16/28

Test Targets

14

Color

Management The wide variety of substrates,

lack of standard ink hues, andunique dot gain characteristicsall contribute to the difficulty of com-

municating and reproducing color by

the flexographic process. Color Manage-

ment Systems (CMS), such as Agfas

ColorTune 3.0 are software systemsused to ensure color consistency among

different input and output devices so

that 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 actual

or expected color results from the print-

ing press.

Because a color monitor can produce amuch wider gamut of colors than the

inks on a printing press, the designer

needs to know the range of printable

colors available on the computer. To

find this range, a color specialist can run

a CMS test on the flexographic printing

press under controlled conditions, using

the same ink, plates, mounting tape, and

anilox rolls required for the actual pro-

duction run. Since each substrate affects

color in a different way, a new test needsto be run for each new type of material.

The results of the test are entered into

the CMS software, which sets up cali-

bration tables and builds press profiles.

Digital cameras, scanners, monitors, and

proofing devices are all adjusted by the

CMS, based on the colors printed by the

individual press. Input devices such as

cameras and scanners, and prepress out-

put devices including monitors andproofing systems are adjusted according

to the predicted outcome on press.

A

B

C

D

E

F

A

B

C

D

E

G

H

I

J

K

L

M

N

A B C D E F1 2 3 4 5

1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3

1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3

1

2

3

4

5

6

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 test

targets. 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 the

press itself. The IT8 7/1, IT8 7/2, and the IT8 7/3 (shown above) test targets all containthe 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 a

color 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 press

profile, the imagesetter is calibrated and the IT8 7/3 file is output to film. Plates are made

and 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 at

each of these devices with the expected output from the actual press run.

There are several color measurement tools used by flexographers to measure printed

samples. Used primarily in the press room, the reflection densitometer can only truly

measure 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 specific

hues of CYMK and base colors used for ink mixing.


17/28

Dot 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, they

tend to grow in size during light expo-

sure. When an ink dot is transferred

from the plate to the substrate, it can

increase in size once again as the inkspreads during absorption. A dot that

began as 50% on film can grow to 51%

on the plate, and eventually print on

a flexographic press as a 65% or greater

dot. The fluid ink and compressible

plates used in flexography tend to

increase dot gain, but it varies according

to the type of press and the substrate.

Smooth non-absorbent films and coated

papers will have less dot gain than

absorbent and irregular surfaces, suchas uncoated papers, newsprint and cor-

rugated liner board.

Dot gain, however, is often consistent

and predictable. Image or color separa-

tion software can adjust dots based on

measurements supplied by the printer.

Typically, the printer performs a finger-

printing analysis, which provides dot

gain information to the color separator

or desktop designer. The IT8 chart onpage 14 shows an example of a test tar-

get used for a press fingerprint. By

printing such a target under controlled

conditions, dots can be adjusted in the

color separation films. In addition, cali-

bration packages built into raster image

processors (RIPs), such as Agfa Calibra-

tor, can also make adjustments.

Even though ink is

transferred under

relatively light pressure

in the printing nip, the

soft flexographic plate

deforms slightly and

compresses duringimage transfer. This

causes ink to spread,

increasing dot gain.

Because harder plates do not com-

press as much as softer plates, they

produce less dot gain. Softer plates,

however, transfer solid images more

completely.

Dot gain can be minimized by usinga thin (0.002"-0.005") capping layer

surface with a higher durometer

than the supporting plate material.

Dot gain can also be reduced by

mounting the plate with compress-

ible tape or a blanket that absorbs

pressure.

An instrument called a Shore A scale measures

plate hardness, which is called durometer. The

image on the left shows the scale measuring a

soft plate; on the right it measures a harder plate.

A higher viscosity ink will not

spread as quickly as one with

lower viscosity. The spreading,or flow-out, of a low viscosity

flexographic ink occurs as it is

transferred to the substrate and

before it dries, contributing to

dot gain. By comparison, litho-

graphic ink is a thicker, paste

consistency, and is not prone to

excessive 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 as

uncoated 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.


18/28

16

Halftones&Screening Halftone Dot Shape

Screen Tints and Gradations

Square dots at 50% Stochastic dots at 20%

Symetrical rounddots at 65%

Asymetrical rounddots at 75%

Asymetrical rounddots reversed at 80%

Offset

lithography

Flexography

Throughout its history, flexog-raphy has been printing qualityline art and spot colors on a

wide variety of substrates. How-ever, it is the recently improved capabili-

ty of high-quality, economical four-color

process printing that has given flexogra-

phy an edge over other processes forpackaging applications.

The Halftone Dot

In flexography, the shape of the halftone

dot used to reproduce a continuous tone

image can significantly affect the density

of the image. Halftone dots can be gen-

erated in a number of shapes, including

square, elliptical, octagonal, and both

symmetrical and asymmetrical dots. At

50% coverage, for example, square dotsproduce a pattern resembling a checker-

board, with individual dots just begin-

ning to join at their corners. When

plates are created from film, dot gain

increases the joining of the dots, which

causes sudden jumps in density in the

printed image, rather than a smooth,

continuous transition.

To minimize the density jumps, printers

can use other kinds of dots that remaindiscreet and retain their shape, even at

coverages of sixty and seventy percent.

A round dot, or octagonal dot are often

used. Though most design software

can specify round dots, selection of dot

shape should occur early in the process

to avoid choosing a shape not available

in the RIP, imagesetter, or platesetter.

Conventional Screen Ruling

Selection of proper screen ruling, whichis critical to four-color processflexogra-

phy, is often dictated by the type of sub-

strate. Anilox cell count and screen ruling

for separations should be correlated

for best results. The cells of the anilox,

which ink a halftone plate, should be

large enough to produce appropriate

To minimize density jumps in halftones,

round dots are preferred. Round dots do

not 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 more

easily controlled or compensated for.

Highlights

Most photopolymer plates are capable of

holding a 2% highlight dot. If plates arent

properly exposed, however, screen tints and

highlight 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 separations

are made. Although printers in offset lithogra-

phy can print acceptable highlights using 5%

film dots, flexographic printers may have to

reduce 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 gradation

without a harsh break at the highlight edge.

When designing images for flexography, it is

best to fade off the end of the design (rather

than to white), or place a border at the high-light end of a vignette.


19/28

Line Screens and Cells Per Inch

Anilox Cell Angles and Halftone Screen Angles

306045

Anilox cell angle

Offset halftonescreen angle 7.5from 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 moir, film or plate

screen 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 prints

halftones screened

at 45, 55, 65, or

85 lpi.

Flexographic

newspaper printers

print halftones

screened between

65 and 100 lpi.

Flexible packaging

on film substrates

is commonly doneat 120 to 150 lpi.

High quality label

printers have the

capability of print-

ing 200 lpi images.

Cells are engraved

on an anilox roll at

one of three angles:

30, 45, or 60.

Screen Ruling

(lpi)

Cells Per Inch

(cpi)

Application

color strength, but not so large that the

halftone dots will dip into them like

an inkwell. For conventional halftones,

resolution is expressed as the number

of lines of halftone dots per inch, also

called screen ruling or lpi. Higher

screen rulings produce higher resolution

images because there are more dots persquare inch used to reproduce detail.

Compare the images in a newspaper

(low screen ruling) to a picture in a

monthly magazine (high screen ruling).

Stochastic Screening

Stochastic, or frequency modulated

(FM) screening, can offer advantages

over conventional halftone screening.

Stochastic screening eliminates the possi-

bility of moir, and also allows theflexographic printer to use HiFi color,

which involves the application of six or

seven process colors.

Dot size used for stochastic screening,

however, is extremely small, comparable

in size to the highlight dot of conven-

tional screening. Since flexography is

subject to significant dot gain, stochas-

tic screening should only be used after

the printer and color separator haveperformed press fingerprints to deter-

mine the ideal dot size and accurate

compensation for dot gain.

The number of lines per inch on the

plate should be no more than 25% of

the cells per inch on the anilox. Ideally,

the anilox should contain a minimum

of 4 cells for every halftone dot.


20/28

Step-and-Repeat&

Die-Cutting

18

Step-and-Repeat

Die-Cutting

Plate Bounce

To save material costs and maxi-mize productivity, the packagingindustry uses a printing technique called

step-and-repeat. Different images,

such as labels, are arranged on the plate

to fill its repeat length and use the entire

width of the substrate when printing.

Often, a technique called nestingwill

be required. Images are strategically

staggered in an arrangement that maxi-

mizes the repeat length and avoids the

plate seam. The plate ends are cut to

accommodate the arrangement. Nesting

can give the appearance of a continuous

repeat, and is used for jobs where all the

images are part of a single roll, such as

gift wrap.

In addition to maximizing substrate

area, staggering images can also avoid a

problem called plate bounce. In flexo-

graphy, images are on the raised areas

of the plate, and can produce a bounce

when coming into jarring contact

with an anilox roll or impression cylin-

der. Bouncing can cause print areas to

skip or misprint if the bounce is away

from the impression, or areas of excess

inking 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 both

the designer and the printer. A die-cut

label or folding carton, for example,

must have all graphical elements in the

correct positions. Packaging engineersoften use Computer Aided Design

(CAD) systems to design folding cartons,

corrugated containers, or rigid paper

boxes; designers may also import the

CAD layout to use as template for

design.

Nesting images can

maximize the plate area

and avoid the plate seam

for step-and-repeat print-

ing. Layout and imposition

software offer step-and-

repeat options for specific

repeat lengths and webwidths.

Bleeds To specify bleeds, the designer

must know where the packaging will be

cut, folded, and joined. In general, bleeds

extend beyond fold and cut lines, but the

precise amount of bleed depends on the

press.

Cut Areas When flexographic printers are

connected to inline flatbed or rotary die-

cutting, the die must be held in register

with the printed colors. Graphic elements

should not be placed too close to cut areas.

Glue & Seal Areas To ensure sealing, glue

areas 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 designer

should make sure that registration is precise.

Varnish-Free Areas Areas that contain

variable information, such as freshness

dates and product coding, must be free of

varnish.

Windows Die-cut windows for folding car-

tons or labels should be clearly indicated,

but may not be available on all die-cutting

machines. Always check with the printer

before 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, and

must allow for dot gain.

Die-Cut Templates Templates can be

exported from CAD systems to illustration

programs, providing the designer with a

two dimensional layout of the job.

Staggering images on

the plate can help keepcontinuous contact between

cylinders, minimizing plate

bounce. Sometimes it is

necessary to place non-

printing bearer bars on

non-image areas to main-

tain contact.


21/28

The Prepress Process

Flexographic Imagesetting Requirements

Accuracy To optimize registra-

tion, output devices should meet

a minimum standard of1 mil

over multiple separations. Geo-

metric and absolute accuracycapabilities are also important

imagesetters considerations.

Size The imagesetter format size

should be large enough to make

the most effective and economic

use offilm, given the particular

application.

Film All film for soft photopoly-

mer plates should be output to

matte emulsion film (minimum

thickness: 0.004"; 0.007" is pre-

ferred). This helps avoid trap-

ping air between the film and

plate during exposure.

Calibration Film dot percentages

below 10% should not vary by

more than 1%; areas over 10%

should not vary by more than 3%.

Uniformity Screen tints should

be a uniform dot percentage,

with no variation in size be-

tween individual dots.

Dot Shape The imagesetter

should be capable of outputting

a hard round dot.

Resolution Resolution shouldbe between 1200 and 3600 dpi.

For line art, solids and type,

1200 dpi is adequate; halftones

require a minimum of 2400 dpi.

Density Film density is an

important factor; imagesetter

exposure 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), the

file is processed by the raster image

processor (RIP) and output to film or

plate. The RIP converts PostScriptTM

data

into a series of bitmapped images. Thelaser output device records this visual

information received from the RIP onto

film or plate material. Larger, more

complexfiles will take longer to process

through 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, jobs

are 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 some

cases, a plate proof is made. A platesetter device essentially follows the same flow with the

exception 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.


22/28

20

Proofing 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 lithography

may not be suitable for different kinds

of substrates, for matching spot colors,

or for reproducingflexographic dot gain.Accurate proofing may require using

two or more methods.

Substrates

Most proofing methods are limited to

a small number of substrates. Because

ink colors are affected by the absorption

and color of the substrate, proofing to

another material cannot provide accurate

color 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 colors

is critical to a job, some printers can

provide a catalog of colors that they can

consistently print on a variety of sub-

strates. Catalogs may contain specially

formulated colors, or use systems similar

to Pantone or FocolToneTM

. Sometimesit is possible to request samples. To

ensure accurate matching, spot colors

should also be evaluated by a color mea-

surement instrument.

Dot Gain

Adjustments for flexographic dot gain

are often not available in proofing sys-

tems designed to mimic the dot gain

found in offset lithography. For this

reason, halftone images and smallertype may not be accurately reproduced

in the proof. However, once a character-

ized profile is established for a given

press using a color management system,

dot gain can be simulated by a digital

proofing 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 not

match CMYK or spot colors printed on the substrate. Higher color

fidelity is possible by calibrating the monitor and by using a color

management 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 proofing

systems. Inexpensive desktop color printers can

also give an approximation of specified colors.

When used with a color management system,

digital printers can provide contract proofs. Most

digital systems are based on CMYK toner applica-

tions, so spot colors may not be accurate.

Most film-based proofing systems are designed to

compensate for dot gain occurring in offset lithogra-

phy. To use these systems for flexography, two sets

offilm must be printed. The first set, which is used

for platemaking, reduces dots to compensate for the

actual 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 have

used a plate proof created on a mounter-

proofer during plate mounting to verify plate

register, quality, and content. Though expen-

sive and not intended for customer approval,

the plate proof today is mostly used on wide

web presses. Plate proofs can be created for

color matching, but they more commonly use

ink hues that are not intended to match press

colors. Color matching from a plate proof is

very difficult due to the differences between

proofing and press equipment.

Printed on the press, a press

proof is the most accurate

method, but because it is also

the most expensive, it is not

common.


23/28

What to Look For During a Press Check

TypeIs the type sharp? Has the weight of the type changed? Witha loupe, look for outline halos.

Registration

Are 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 therepinholes or voids? Under a loupe, halftone dots shouldappear sharp, not slurred.

SubstrateIs the width, caliper, and type of substrate as specified? Ifthe 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 pressoperator may be able to relieve some pressure; some platesmay have spot color inaccuracies that require a plate remakeor remount.

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

UPC and Bar CodingOver-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 ensureaccuracy. Makeready on a flexographic

press includes installation of the required

plate cylinders and inks, setting levels

for impression and ink pressure, register

adjustment, and any setup for inlinefinishing, such as cutting, folding, or

gluing. Pressure levels are particularly

critical for accurate printing. Finally,

after press adjustments are complete, the

press operator checks colors for the job,

running a sample at (or near) produc-

tion speeds. Designers should also make

sure to perform a press check for the first

actual 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 plate

elongation 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 accurately

mounted, the job should be in register.

Traps

Have plate mounting and plate elongation

maintained accurate trap areas?

Bar Coding

Have the bar codes been positioned to

allow proper open area surrounding the

code for scanning? Has the bar code been

positioned with the bars parallel or per-

pendicular to the web direction? When

mounted perpendicular to the web direc-tion, bar codes will be affected by plate

elongation.

Wind Direction

Has the job been set-up to print in the

right direction on press? Will the print

direction match the packaging or labeling

operation?


24/28

22

Glossary&Index

design roll: 2, 8

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

die-cutting: 18

The process of using sharp steel rules to cut

shapes for labels, boxes and containers, fromprinted sheets. Die-cutting can be done oneither flat-bed or rotary presses. Rotary die-cutting is usually done inline with printing.

direct-to-plate: 8

The process of using digital information tolaser image a printing plate or design roll, bypassing the film stage of production.

distortion: 9

Intentional compensation for flexographicplate elongation.

distortion factor: 9

A percentage number calculated by a plateelongation formula and applied to imagesprior to output offlexographic films.

dot gain: 15, 16

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

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

dry trapping: 12

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

dual doctor ink chamber: 4, 6

On aflexographic press, a cartridge designed

to supply ink to the anilox roll in an enclosearea. 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: 8

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

anilox: 5, 6, 17

An 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: 4

In 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: 18

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

calendered paper: 10

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

caliper: 10

Thickness of a substrate, usually measured inthousandths of an inch.

cell angle: 6, 17

On an anilox roll, the measure of a linedrawn through the center of a row of cells

and a line drawn parallel to the shaft of theanilox. The angle at which cells are arrangedon an anilox roll.

cells per inch (CPI): 4, 17

On an anilox roll, the number of cells in alinear inch.

cell volume: 6

A 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 a

technique known as infratometry.

choke: 12

A 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: 14

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

color management system (CMS): 14

A 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, 7

A printing press configuration that positionsall color decks around a central impressioncylinder. The CIC press configuration offers

web support throughout the printing opera-tions, and optimum registration capabilities.

computer aided design (CAD): 18

Electronic equipment used by package designengineers to layout and design in threedimensions the structure of a package.

continuous repeat: 7

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

contract proof: 20

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

converting operations: 7

In packaging, any process performed to man-ufacture a completed package from a rawmaterial or an unfinished material.

corrugated: 6, 7, 10

The combination of linerboard and corrugat-ing medium as afluted material.

corrugated press: 2, 7

An inline sheet-fed press (usually aflexo-graphic press) designed for printing sheetsof corrugated.

cut areas: 18

In 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: 5

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


25/28

durometer: 15

A measure of the hardness of rubber. Themeasuring instrument most widely used isaShore A durometer gauge.

fingerprint: 12, 14, 15

A method of testing characteristics of a print-ing press by use of a test plate.

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

fountain roll: 6

In 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: 4

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

freesheet paper: 10

Paper free of mechanical wood pulp.

gradation: 14

A smooth transition between shades.

gravure: 2, 4

An intaglio printing process that uses anengraved plate as a master image carrier.Gravure is used for printing packaging,speciality products, and publications.

HiFi, high fidelity: 11, 17

A method of increasing the process colorprinting gamut by printing six, and some-times seven, process colors.

image carrier: 4

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

impression cylinder: 4, 6

The cylinder that provides web support dur-

ing image transfer from plate to substrate.

inline finishing: 7

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

inline press: 6, 7

A multicolor press where the printing unitsare assembled on a common plane, or inline

with one another. Also refers to any combi-nation of printing and converting operationdone simultaneously.

intaglio: 4

A process in which the image is recessed

below the non-image area, used in gravureand steel die engraving.

kraft linerboard: 10

A type of paper made from chemicallypulped wood fibers, and used as the topand bottom layers in a sheet of corrugated.

kiss: 6

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

laser ablation: 8

A 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, 4

A method of printing from a plane surface(such as a smooth stone or metal plate) on

which 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 from55-300. Originally, halftones were made by

placing 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: 10

Paper 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 a

web of paper around a chilled roller andover the point of vaporization. Vaporizedmolecules collect on the cool web, giving thepaper or film a metallic finish.

moir: 6, 17

A repetitive interference pattern caused byoverlapping symmetrical grids of dots or lineshaving a differing pitch or angle.

mounting tape: 9

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

nailhead: 12

In 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: 6

The 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 differentiates

wide web from narrow web.

nesting: 7, 18

A technique of placing images between otherimages on aflexographic step-and-repeatlayout. Nesting is done to minimize substrate

waste, and/or to minimize flexographic platebounce.

nip: 6

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

offset lithography: 4

Planographic print using an intermediateblanket cylinder to transfer an image fromthe lithographic plate to the substrate.

over-impression: 13, 15

In aflexographic press set-up, excess pressurebetween the plate and the impression roll.

paperboard: 10

There 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: 8

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

planographic: 4

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

plate elongation: 9

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


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24

Glossary&Index

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 aflexographicplate cylinder coming in contact with theanilox or impression roll.

plate proofs: 20

A 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: 9

A measure of the height of aflexographicplate from the back to the top of the imagearea, usually expressed in thousandths of aninch.

polyethylene films: 2, 5, 10

Thin clear substrates used as packagingmaterials, commonly known as plastic as inplastic bags.

polymer films: 10

Any one of a number of different non-absorbent, thin, clear, or colored substratesused as packaging materials, and commonlyreferred to as plastics.

printing plate: 4

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

proof, proofing: 20

A 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): 19

The computerized process that results in anelectronic bitmap which indicates every spotposition on a page in preparation for actualprintout.

reflection densitometer: 14

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

relief: 5

In printing, a process that prints from raisedimage areas.

repeat length: 7

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

resolution: 16, 17

The measure offineness 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: 11

Printing the underside of a clear substrate.Sometimes called back printing.

run-length: 5

The 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: 10

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

spectrophotometer: 14

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

spot color: 11

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

spread: 12

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

stack press: 7

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

step-and-repeat: 18

In 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: 17

Also called frequency modulated or FM

screening. An alternative to conventionalscreening that separates an image into veryfine, randomly placed microdots, rather thana grid of geometrically aligned halftone cells.

substrate: 4, 10

A material on which print or coating isapplied, such as paper, polyethylene, or foil.

trap, trapping: 12

In prepress, a technique which allows forvariation in registration during the press runOn the desktop, this is done primarily by allowing an overlap between abutting colors.

variable repeat length: 7

In printing, the capability of a printing pressto print from various size plate cylinders or

printing plates.

vignettes: 16

An image in which the background fadesgradually away until it blends into theunprinted substrate.

wet-out: 10

The tendency of an ink to level-out as woula true liquid. On a substrate, an inkfilmshould flow and level itself rather than beading

wet trapping: 12

The technique of printing multiple colorswhereby each succeeding inkfilm remainsopen (not dry) as the next color is appliedon or over it.

white back-up plate: 11

A printing plate made for applying a solidwhite ink as a reflective base under all coloreimages on a clear substrate.

wide web: 6

The lower limit of wide web flexo has beenspecified to be as narrow as 18" or as wide a32" by various sources within the flexographic industry. There is presently no agreementon the exact cut-off width that differentiates

wide web from narrow web.

windows: 18

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


27/28

Working With Prepressand Printing SuppliersDigital Color Prepress - Volume Three

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PostScript ProcessColor Guide1996 Edition

This 52-page oversized reference containsover 17,000 electronically created CMY andCMY+K process color combinations (oncoated and uncoa

flexo and packaging

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