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graphy is now the fastest growing printing

process in the world.

Successful packaging catches the cus-

tomer’s eye. Manufacturers know that estab-

lished brands need consistent color match-

ing and print quality to attract attention on

store shelves and to help assure customer

loyalty.

To boost sales, manufacturers are relying

heavily on full process-color printing. Full

process-color printing is a system of repro-

ducing a variety of colors by printing three

standard-color inks in various combinations

and proportions, usually with black added.

For example, the process color images

depicted on frozen food packages must look

real, appear appetizing. If the color looks arti-

ficial because of poor printing, sales could

suffer. It is evident that flexographers and

manufacturers will continue to be partners,

especially in the printing of plastic bags for

food packaging.

Until recently, flexography was rarely

involved in the printing of publications, but

the process is now making inroads in this

area. Flexographically printed comics and

inserts are being produced with excellent

results. Water-based inks that produce a no-

INTRODUCTION 5

■ Prints on a wide variety of absorbent and nonabsorbent substrates.

■ Prints on the reverse side of stretchable, transparent films.

■ Prints using resilient rubber or photopolymer image carriers – millions of impressions can be printed.

■ Allows printing of 10 or more colors because of multiple print stations.

■ Allows continuous pattern printing (giftwrap, wallpaper, floor coverings) because of its near-total vari-

able-repeat-length system.

■ Can achieve press speeds of 2,000 feet per minute or more (certain segments of the industry).

■ Prints process color jobs 175-lpi and higher (smooth-coated substrates).

■ Uses fast-drying solvent, water-based or UV curable inks.

■ Eliminates back-trap contamination, setoff and trapping problems by allowing wet ink to print over dry

ink.

■ Can deliver a predetermined amount of ink with minimum on-press adjustments with its inking system.

■ Can print using flourescent and metallic inks.

■ Allows printing-plate cylinders to be taken out of the press to enable printing plates to be mounted

and proofed as a prepress operation.

■ Can perform coating and in-line operations such as laminating and diecutting as a continuous opera-

tion.

■ Can produce the complete package, such as folding cartons, displays, multiwall bags, labels, in-line.

■ Is cost effective for many applications.

■ Offers high investment return on equipment.

■ Enables fast turnaround time between jobs.

■ Can make short-run work more profitable.

CHARACTERISTICS AND ADVANTAGES OF FLEXOGRAPHY

6 FLEXOGRAPHY: PRINCIPLES & PRACTICES

rub-off image on thinner newsprint have

been well received. Interest in flexography is

now global. The 1990s have seen major

improvements in flexo print quality.

New products and new packaging contin-

ue to evolve. It is a challenge for flexography

to keep pace. Makers of presses and related

equipment are designing with state-of-the-art

advances in mind. Vendors and supplies also

are obliged to keep abreast of new technolo-

gy as standards for print quality get tougher.

In the corrugated area, many companies

are preprinting linerboard, roll-to-roll, using

process colors with great success. The

preprinted rolls are then combined with tra-

ditional corrugated medium and die cut,

folded and glued, either in-line, or later, off-

line. The finished carton has enhanced eye

appeal and excellent print quality.

Traditionally, corrugated printers used

sheetfed letterpress presses when working

with combined board. It has always been dif-

ficult to achieve decent print quality and

image sharpness without crushing the flutes,

which reduced the strength of the case. But

flexo, using water-based inks to print direct-

ly onto combined board, has been on the rise.

The quality of corrugated postprint using

flexography is limited only by the initial

quality of the combined board. The quality of

graphics printed on combined corrugated

board, using state-of-the-art presses, is rival-

ing that of offset preprinted labels.

Flexography can expand in many different

directions. It has grown into a sophisticated,

high-quality process of choice.

OTHER PRINTING METHODS

Flexography is the predominant method

of printing in the packaging industry and is

expanding in other printing segments. This

section provides a short overview of other

major printing methods, including some

hybrid ones, such as those that combine dif-

ferent printing methods on one print station.

Letterpress

Letterpress was the first printing method,

and its name pretty much describes how it

works. The relief printing surface of the type

is inked with a paste ink and literally pressed

onto the paper. The main characteristics of

letterpress are clear, crisp impressions and

strong, vibrant colors.

It made its first mark in history, when

Johann Gutenberg, in the 15th century, pro-

duced a two-volume Bible. Ironically, this

venture bankrupted him, but the printing

process continued its growth.

During the 1700s, America’s independence

was owed in part to the use of letterpress, as

Ben Franklin and Peter Zenger were printing

materials that supported our freedom.

Until the late 1800s, letterpress was the

only printing method around. Offset, gravure

and screen printing did not appear until after

the turn of the century. In the 1950s, offset

printing got started and eventually became

the major printing process of our time. In the

1980s, letterpress’ share of the market

declined, and web-offset replaced it at most

newspapers and magazines. In general,

small jobs could be done on high-speed off-

set duplicators or electrostatic copiers.

Letterpress is now limited mainly to spe-

cialty work, such as numbering, embossing,

hot stamping and hot-wax carbonizing (spot-

carbon printing). It is also used for die cut-

ting, perforating, slitting and scoring.

Since the introduction of photo-composi-

tioned type, hard photopolymer or rubber

plates took the place of the old hot-metal

linotype casting machines. Most letterpress

type forms were replaced by one-piece alu-

minum or steel backed photopolymer mate-

rials. Today, very few printers use handset

foundry or hot-metal type.

In the press, lead- and trail-sheet lockup

systems, magnetic bases or magnetic cylin-

ders are used to hold plates in place. Most

letterpress printers are using photopolymer

or rubber plates instead of the original hard

metal plates. Letterpress is also used for hot

foil stamping, where a heated metal printing

plate melts glue on the back of the foil sheets

transferring the characters to the substrate

being printed.

Typical letterpress configurations are plat-

en, flat-bed with impression cylinder and

rotary (Figure

On a typical rotary letterpress print station

used mainly on newsprint presses, the print

station includes an ink fountain and a steel

fountain roller turning in contact with the

thick paste ink (Figure

). Notice the many

rollers in the inking train. The ink is picked

up by a roller that conducts the ink to a series

of oscillating/rotating steel rollers with rub-

ber rollers in between. The ink is thinned out

and transferred by the rubber form rollers

which in turn ink the type or printing plates.

The image is pressed into the substrate

against an impression cylinder, which is cov-

ered with a rubber blanket or tympan paper

(a soft, makeready packing paper).

The sharp image for which letterpress is

noted is slightly embossed below the surface

of the substrate. For fine-line screen printing,

a smooth substrate is essential; the smoother

the substrate, the greater the detail.

Letterpress is limited to 150-line screen work.

As with flexo printing, letterpress requires

some pressure to the substrate to transfer

the image. While flexo plates are relatively

soft and displaceable, letterpress plates are

hard and require more pressure than flexo.

Many printers mistake flexography as a

form of rotary letterpress. Flexo plates look

like relief-letterpress plates, but that’s where

the similarity ends. Flexo uses a “kiss”

impression with fast-drying fluid inks.

Letterpress uses slow-drying paste inks and

cannot print on plastic films or many of the

other materials that flexo handles with ease.

Lithography

Lithography prints from a flat (plano-

graphic) surface.

In 1798, Alois Senefelder discovered the

basic principle of lithography, when he

wrote on a flat stone with a grease pencil. He

dampened the limestone surface with water

and inked the writing with a greasy ink, then

pressed the paper against the stone, trans-

ferring the inked image to the paper. The

image, of course, printed in reverse.

What happened was this: The water wet-

ted the nonimage areas on the stone but was

repelled by the greasy image areas.

Conversly, the greasy ink was repelled by the

wetted areas of the stone and was only

attracted to the image areas. Later,

Senefelder wrote on paper with a greasy ink

and then pressed the image to the dry stone

surface. In doing so, the image reversed

itself when transferred to the stone. He wet-

INTRODUCTION 7

Typical letterpress

configurations are

platen (a), flatbed (b),

and impression

cylinder (c).

A typical rotary

letterpress print

station used mainly

on newsprint presses.

The print station

includes an ink fountain

and a steel fountain

roller turning in contact

with the thick paste ink.

Web

Plate

Cylinder

Inking

Train

Ink Tray

Impression

Cylinder

8 FLEXOGRAPHY: PRINCIPLES & PRACTICES

ted the stone and inked the reversed greasy

image. When he pressed paper to the stone,

the image it produced was the first readable,

direct stone lithographic print ever.

For generations, a special Bavarian lime-

stone was used for the image-carrying

“plate” from which the process got its name,

taken from the Greek words “litho” (stone)

and “graphein” (to write).

Today, stone lithography is very rare and is

only being utilized by a small group of pro-

fessional artists who produce limited edition

prints. At one time, zinc coated with a photo-

emulsion was widely used. The images were

rubbed off the zinc plate with abrasives,

dried, recoated with emulsions and reused.

Most modern lithographs are made from

thin aluminum plates.

Printers buy presensitized aluminum

plates that they expose through negatives,

using vacuum contact, under bright light.

After exposure, the latent image is devel-

oped with a greasy developer and dried. On

press, the aluminum plate is dampened with

a water fountain solution and inked by rub-

ber form rollers. Faithful to the process, only

the ink is attracted to the image, since the

water repels it from the nonprinting areas.

The thin-gauge aluminum plates are relative-

ly inexpensive and are not reuseable but

may be recycled for the aluminum content.

In some cases for short-run jobs, plastic-

coated-paper printing plates covered with a

photo emulsion are used.

The image is positive-reading on the plate

surface. Both the inked image and nonprint-

ing areas are on the same plane, hence the

name planography. The plates are attached

to the plate cylinder by clamping the plate’s

leading and trailing edges, leaving a gap

between the clamps, which makes continu-

ous-design patterns impossible to print with

this process. Only flexography and gravure

use an uninterrupted cylinder surface that

allows continuous patterns to be printed.

As the plate cylinder turns, it is dampened

with a water-wetted roller and immediately

inked (Figure

). The plate cylinder then

comes in contact with a rubber-blanketed

cylinder. The positive printing plate image is

transferred or “offset” to the blanket surface

in reverse. The blanket in turn transfers the

image to the substrate against an impression

cylinder in positive, readable copy. Offset

presses can be either sheetfed or web-fed.

Historically, offset presses have been

sheetfed. Web-fed offset presses first

appeared in the 1960s. Out of a need for high-

er press speeds, most publication worktoday

is being done with web-offset. Lithography

has been a favored process because it can

reproduce soft tonal values on coated sub-

strates. Another highly-prized feature of lith-

ography is its ability to print 300-line screen

images with excellent fidelity.

Rotogravure

True intaglio or steel-die process prints

from sunken lines or grooves are connected

and cross each other. Ink is then applied to

the engraved areas and doctored or wiped

off the smooth nonimage areas. The result-

ing inked image is then impressed onto the

substrate to be printed. Our paper currency

is printed from steel dies capable of repro-

ducing very fine lines that no other process

can duplicate. Rotogravure is a form of

A typical offset litho-

graphy print station.

The print station

includes the inking

train and water rollers,

the plate, rubber blanket

and impression

cylinders.

Web or Sheet

Rubber

Blanket

Cylinder

Inking

Train

Ink Tray

Water

Pan

Impression

Cylinder

Plate

Cylinder

“intaglio” (cut-in or sunken) printing and

prints directly from unconnected cells

engraved into the plate cylinder.

The print cylinders in gravure are

machined, electroplated with copper, ground

and polished. For photo-etching the cylin-

ders are then coated with a light-sensitive

emulsion. After drying, negatives are con-

tacted completely around the cylinder and

exposed to light. The sunken cells are etched

into the cylinder with an iron chloride solu-

tion. To increase the run length of the copper

cylinder, chrome plating is applied over the

copper to protect and harden the surface.

For short runs, the copper cylinder may be

used without chrome plating.

In place of the photo-etching process, an

electronic scanning machine with a diamond

stylus can be used to mechanically “deboss”

copper cylinders in place. Most recently the

use of computer-driven laser etching images

directly to the surface of ceramic coated

cylinders is replacing the former technology.

In gravure, the cells holding the ink are not

interconnected, therefore a checkerboard or

saw-tooth pattern shows up around print

edges – a characteristic of gravure printing.

To overcome this deficiency, very fine screen

sizes are used to make the rough edges as

inconspicuous as possible. The cylinder’s

print areas are etched as microscopic, cup-

like cells, while nonprint areas remain

untouched. The larger and bolder the copy,

the larger and deeper the etched cells. Fine

tonal areas have a smaller cell size and depth.

Gravure inks are fluid and have very low

viscosity. They are formulated of resins dis-

solved with solvents, pigments and addi-

tives. On press (Figure

), the image-bear-

ing cylinder is either flooded with an appli-

cator roll or rotates in an ink pan, or foun-

tain, in order to fill the cells with ink. Excess

ink on the surface of the cylinder is wiped

off with a steel doctor blade. As the cylinder

makes contact with the substrate, ink leaves

the cells by capillary action to transfer the

image to the substrate. Often the ink will not

release from the cells to the web substrate,

causing print “skipping.” To overcome this

deficiency, a rubber roller provides an elec-

trostatic charge to the system. This helps

eliminate skipping by allowing the electro-

statically charged ink in the cells to be

attracted by an opposite charge in the roller.

Gravure inks must be free of foreign parti-

cles. These can cause streaking on the cylin-

der surface, resulting in doctor-blade streak-

ing on the printed web. If streaking does

occur, the cylinder has to be removed from

the press and refinished. If the doctor blade

has nicks or other defects, the blade must

either be replaced or reground to a smooth

finish.

Most gravure presses are web-fed (roto-

gravure). But some are sheetfed and have a

flat plate that clamps to the plate cylinder.

Other gravure systems use removable

sleeve-type cylinders. Presses are mostly

inline, designed with a dryer unit above each

print station. The web travels from one print

station to another with wet ink overprinting

dry ink throughout the process. Six- to eight-

color presses are common.

Gravure is used to print line work and fine

halftones at relatively high speeds, and print

runs can go into millions of impressions. Run

length depends on the condition or wear of

INTRODUCTION 9

In a typical gravure

print station, the ink

station includes a

gravure cylinder flooded

with low-viscosity ink,

which is doctored and

then transfers the ink

to the substrate.

Rubber

Impression

Cylinder

Web

Gravure

Image

Cylinder

Doctor

Blade

10 FLEXOGRAPHY: PRINCIPLES & PRACTICES

the print cylinder, and the streaking men-

tioned above would certainly shorten a cylin-

der’s life.

Ideal substrates for gravure are smooth-

finish, clay-coated papers, super-calendered

papers, rigid films and foils. Since effective

ink transfer depends on thorough cell con-

tact with the substrate, irregular or “toothy”

rough surfaces are generally not printed

gravure. Stretchable substrates also present

problems with registration and print quality,

while thick or rigid films print quite well.

Gravure is used for packaging, magazines,

newspapers, and other specialty printing

applications. It has been an outstanding

choice for printing process color for mass-

circulation magazines and newspapers.

Gravure-printed postage stamps are another

example of the fine print results of

rotogravure. Many plants have blended flex-

ography with gravure to produce exception-

al print results on packaging materials.

Screen Printing (Serigraphy)

Screen printing or screen process printing,

originally known as silk screen printing, first

appeared in ancient China, where silk was

abundant. Today, man-made fabrics and

stainless steel are used for the mesh screens,

so the word “silk” has been dropped.

The basic equipment includes a table, a

rigid frame, a finely meshed screen, a semi-

rigid squeegee, stencil materials and heavy,

viscous ink (Figure

). The process

involves using a squeegee made of wood or

rubber to force ink through a porous, screen

stencil to a substrate beneath.

In the beginning, screen stencils were

hand-cut from a special, lacquered film

material, but the process was slow and inef-

ficient. Today, there is a choice of using

either computer-aided, mechanically pro-

duced stencils or the more popular direct

photo-emulsion variety. In the latter process,

the screen is strectched tightly over the

frame, and a photo-emulsion is applied to it.

Film with a positive image is put into vacu-

um contact with the screen’s dry emulsion

and exposed to white light. After exposure,

the image is washed out with a water spray.

The unexposed areas are insoluble and wash

out cleanly; while the exposed areas are

painted with a block-out solution to prevent

ink from bleeding through the screen. The

screen is attached to a table on one side by

clamps or hinges, or installed in an automat-

ic press location. The screen becomes the

image carrier. Printers currently use durable,

ultra-fine stainless-steel mesh screens that

are capable of reproducing remarkable read-

able 6 pt. type, along with intricate designs.

The substrate is positioned under the

screen and frame. Register tabs are located

on the table, or press guides are set in place

on the feed table of the press to register each

sheet for printing. The screen is lowered and

ink is deposited at one end. Then, the

squeegee is pressed down and across the

length of the screen, forcing the ink through

and printing the image.

The ink-film thickness on the substrate is

approximately equal to the thickness of the

screen’s fabric filaments. For fine-line

process color work, fine threads or filaments

are used, and multiple colors can be printed.

The photo stencils can be removed with sol-

vent sprays after use and the screens reused.

For a typical screen

print station, the ink

station includes a

screen in a frame and

squeegee to force ink

through the screen

onto the substrate.

Squeegee

Ink

Finished

Stock

Frame

Printing

Stock

Stencil

Open

Screen

Both single and multicolor presses are

used. Many require an operator to insert and

remove the sheets by hand. Some have auto-

matic squeegee impression cycles. The fully

automatic machines feed the sheets, register

colors, lower the screen and squeegee the

print. The sheets are removed to a dryer and

then stacked at the other end of the press.

Some presses use round, brass screens.

These print dyes to fabrics from a roll. In-

line presses print from one station to anoth-

er for eight or more colors. The process is

simple and lends itself to many specialty

applications.

Through the use of specially built jigs and

printing frames with flexible screens, the

silkscreen process is widely used for print-

ing rounded and irregular surfaces such as

bottles, tubes, plastic and metal objects. The

chief advantage of screen printing is its ver-

satility on many different surfaces, irregular

or flat. Screen printing also lays down a

smooth, heavy ink-film thickness. Many out-

door reflective signs, like those used on

highways, are screen printed on metal.

Indeed, many items are screen printed

because they can not be printed any other

way. The process is ideal for short-run jobs.

Letterset (Dry Offset)

Water used in the offset process some-

times causes problems because of the criti-

cal balance that must be kept between it and

the oil-based ink. The letterset or dry offset

plate system was introduced to eliminate the

need to dampen the plate with water. A hard,

shallow-relief letterpress plate is used to

print to the blanket on an offset press.

(Figure

). As the name implies, letterset

means the use of letterpress plates on an off-

set press.

Offset Gravure

Offset gravure is a combination of offset

lithography and rotogravure. In convention-

al offset, the flat offset-plate image has a lim-

ited life and can wear off during long runs.

To overcome this, a longer-wearing gravure

cylinder can be used instead. The gravure

cylinder transfers its image to an offset blan-

ket with excellent fidelity (Figure

). The

image on the gravure cylinder must be posi-

tive so it can transfer a reversed image to the

offset blanket. In turn, the blanket’s image

prints positive on the substrate.

Coarse surface substrates or even woven

fabrics are printed with surprising fidelity

overcoming the need to print on super-cal-

endered or coated papers using standard

rotogravure. With or without electrostatic

help, the ink easily transfers its image to the

smooth rubber blanket. In doing so, the

image from the blanket faithfully delivers its

minute dots to the substrate.

INTRODUCTION 11

The typical letterset –

also called dry offset –

print station is similar to

offset but eliminates the

use of a dampening

(water) system by using

a shallow relief plate.

In a typical offset

gravure print station,

the gravure cylinder

transfers ink to the

offset blanket.

Web

Plate

Cylinder

Rubber

Blanket

Cylinder

Inking

Train

Ink Tray

Impression

Cylinder

Impression

Cylinder

Web

Engraved

Gravure

Cylinder

Rubber

Blanket

Roll

Doctor

Blade

12 FLEXOGRAPHY: PRINCIPLES & PRACTICES

Flexo Offset

In this process, a flexographic printing

plate is used in place of the gravure cylinder.

The flexo plate, with a positive image, prints

to the offset blanket, which reverses it and

prints a positive image to the substrate, as

shown in Figure

Round, plastic containers are printed this

way. Some special presses have three- or

four-color stations around the offset blanket

cylinder. All the colors are registered on the

surface of the blanket, which transfers the

multicolored image directly to the rotating

container during each revolution.

The containers are held by vacuum on a

printing spindle. After one is printed, the

next, on its own spindle, comes into position

and is printed. Aluminum cans with a clear-

base coating and tapered drinking cups can

also be printed this way. There are still many

untapped applications for flexo offset.

The typical flexo offset

print station requires the

flexo plate to transfer

ink to the offset blanket.

Web

Plate

Cylinder

Doctor

Blade

Offset

Blanket

Anilox

Roll

Impression

Cylinder

here have been many critical

events, inventions and other fac-

tors that influenced the evolu-

tion of flexography. What fol-

lows reflects some of the known

milestones in the development

of flexographic printing.

ANILINE PRINTING

Aniline printing, as flexography was

known until 1952, evolved out of rotary let-

terpress. Its name was taken from the ani-

line dyes in the inks that were used at the

time.

Early forms of the aniline press were in

use in Europe as far back as 1860, and histo-

rians trace the first modern style of aniline

press to 1890, when Bibby Baron and Sons

of Liverpool, England, built what resembled

a central-impression cylinder press, with

printing units around the drum.

The first patented aniline press was pro-

duced by C.A. Holweg of Alsace-Lorraine,

who was granted British patent #16519 on

November 7, 1908. Holweg built the stack-

type press in 1905 as a tail-end printer unit,

in-line with a bag-making machine. Since the

alcohol dyestuff ink dried so quickly, it was

possible to produce bags in a continuous

operation after printing. Another key player

during the infancy of aniline printing was

Strachan and Henshaw in Great Britain, pro-

ducing central-impression presses.

Windmoeller & Hoelscher GmbH of

Germany sold presses for printing bags.

These machines used inline with aniline

presses that produced paper bags in one

continuous operation.Its popular bag-mak-

ing machine, introduced in 1914, was called

the “Matador.”

Also in the late 1800s, Francis X. Hooper

designed and built a press for stamping ink

identification marks onto the wooden

planks of shipping crates, using metal type

known as “printing dies.” Hooper’s presses

were very much like the more modern print-

er-slotter. Around the turn of the century, the

George W. Swift Company developed aniline

presses that could print on fiberboard.

By 1900, combined corrugated board was

being considered as a shipping box material.

In 1914, the Interstate Commerce Commis-

sion decided to allow the use of corrugated

boxes for interstate commerce, thus inaugu-

rating a huge industry in the United States.

Presses soon appeared that could die cut

after printing and add slots and creases to

the corrugated box. Previously, dried, print-

ed corrugated boxes were folded without an

overlap on the corner and automatic taping

machines were marketed during the 1920s

and 1930s.

The early corrugated printers saw the

need for flexible, displaceable plates that

would not crush the fluted material. Presses

had to be built to handle the various calipers

of fluted board and 0.250" thick printing

plates which were nailed or tacked in place

on the wooden print cylinders. For many

years, only letterpress paste inks were used.

Ink drying was slow, causing die-cutting and

INTRODUCTION 13

The Evolution of

Flexography

14 FLEXOGRAPHY: PRINCIPLES & PRACTICES

finishing delays. The need for a faster-drying

ink system became apparent.

Ink metering for early aniline printing was

achieved using two rubber rolls; one to draw

the ink from the ink fountain, the second to

doctor the ink film and transfer the ink film

to the printing plate. At this time, printing

plates were either wooden or metal, similar

to those used in letterpress or hand-

engraved designs, drawn or traced on sheets

of prepared vulcanized rubber compounds.

EARLY DEVELOPMENT

The early development of aniline printing

ran head-on into the “do-it-yourself” age.

Many converters designed and built their

own equipment using local machine shops to

fabricate their designs. Most presses were

simple and followed the design for stack

presses. Many made their own rubber plates

and dyestuff inks. These homemade presses

were of light construction, with the printing

stations consisting of an ink pan, a rubber

fountain roller, rubber ink-transfer roller and

a plate cylinder with an impression cylinder.

Ink metering was crude and uncontrolled.

Two rubber rollers, or an aluminum together

with a rubber roller, were used to ink the

plates. Ink-film thickness on the plates varied

and was unpredictable. An increase in press

speed caused more hydraulic force between

the rollers and over-inking, resulting in crude

and fuzzy printed images.

In the 1920s, aniline ink was made from

water-soluble, coal-tar dyestuffs. The dyes

were dissolved in alcohol, with tannic and

acetic acids added, to make them smear-

proof. They had very poor light-fastness and a

short shelf life; they also bled into the surface

of paper substrates and migrated with

uncoated cellophane. Even after drying on

the substrate, they had a very unpleasant

residual odor which could contaminate food.

In the early 1930s, titanium-dioxide-white-

pigmented ink, pigmented yellow and orange

inks appeared. Metallic inks also arrived, in

addition to colors such as red, green, blue

and black. By 1938, water-type opaque inks

were developed for printing on paper, paper-

board and combined corrugated board. Until

the 1950s, only dyestuff, alcohol, water-solu-

ble and some pigmented inks were available

to the aniline or flexographic printer.

By the 1940s, aniline presses were print-

ing about 150 feet per minute. Within 10

years, press speeds increased, forcing ink-

drying speeds to increase through new ink

technology.

INTRODUCTION OF THE

ANILOX ROLL

In 1939, a mechanically engraved, chrome-

plated, ink-metering roll was introduced in

the aniline industry. Similar to rotogravure

print cylinders, anilox rolls were produced

by mechanically engraving the surface of

copper-coated rolls with a controlled pattern

of ink-carrying cells. Chromium was then

electroplated over the copper layer to pre-

vent corrosion and increase wear resistance.

The name anilox roll was derived from the

aniline process.

Then, as now, the anilox roll is the heart of

the flexographic printing system. Its intro-

duction was a milestone in the development

of an accurate inking system, and the older

rubber-roll-to-rubber-roll system began to

disappear.

IMPACT OF MAN-MADE PLASTICS

The introduction of polyethylene to the

packaging industry as an alternative to cello-

phane marked another milestone in the

industry. New substrates affected press

design. Once polyethylene came along in the

1940s, presses had to be refined to work with

this stretchable material. It caused radical

changes in web-tensioning devices, unwind

and rewind controls, edge-guiding equip-