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206 FLEXOGRAPHY: PRINCIPLES & PRACTICES

the ink pan to rewet the dried ink in the

pan. Concentrate on areas where ink

buildup exists, rewetting the rag as

needed.

4. Wipe the ink pan dry using a second

rag when all ink buildup is removed.

Only a haze should remain.

5. Dampen another clean rag with clean-

ing solution to remove the remaining

pan haze. Immediately use a dry rag to

give it a final shine.

6. Use the two rags to clean the outside

of the pan and deck cover.

7. Remove the ink return hose. Wipe any

remaining ink out of the drain hole.

Label Ink Containers

The containers holding the ink used dur-

ing the run should be marked with the cor-

rect ink color and/or number. Any addi-

tives, bases or solvents that were added to

the ink, and their quantities, should be

noted on the containers.

Dirty cleaning solution must be removed

from the press and poured into a waste dis-

posal container where it will be recycled or

disposed of as hazardous waste.

Remove Unprinted Stock

Unprinted stock should be labeled and

returned to its assigned storage location.

Clean Tools and Press Area

All pH meters, viscosity cups and other

tools used during the pressrun should be

cleaned and prepared for use on the next

run. All spills and splashes around the

machine should be wiped up, not only for the

sake of appearance, but for safety as well.

Clean the Pumps

If submersible pumps are used, the opera-

tor should place the pump in a bucket of

cleanup solution and flush out the pump and

hoses. After flushing with cleanup solution,

the pumps should be flushed with fresh sol-

vent or water. Repeat these steps for each

printing station.

PRESSROOM PRACTICES 207

Corrugated

Press Procedures

he procedures for a corrugated

flexographic press setup, run

and cleanup vary depending on

the press manufacturer, the age

of the press and the different

methods used by printers. For

this reason, this section focuses on the

basics of setup that are common to most

corrugated printers.

PRESS SETUP

Corrugated press crews typically make

several setups each day. Each setup must be

made in the most time-efficient manner pos-

sible. In order to achieve a high level of effi-

ciency, it is important for the crew to look

ahead to future orders. Looking ahead allows

crews to coordinate the colors being run

from print station to print station and the

type of board being run. This coordination

creates better efficiency because the press

should not need to be broken down as much,

and only the stations to be changed need to

be washed for the next order. Crews must

plan ahead to have the next order’s ink, stock

and other materials ready before the existing

run is finished. Running a corrugated press

requires good communication and thorough

planning between the crew members.

Supply Assurance Precheck

A supply assurance precheck should be

completed prior to press setup. The follow-

ing items detail a typical precheck. All items

should be available and reviewed by the

crew before press setup:

Shop orders. Sometimes referred to as job

instructions, work orders or job jackets, this

order contains all of the instructions needed

to produce the finished product to the cus-

tomer’s specifications.

Print card. Sometimes called a print copy, this

card is a part of the shop order. It contains

specific instructions for the job being print-

ed, and provides information on dimensions,

position, color and quantity (Figure ). In

most cases, the card also contains a graphic

layout of the job.

Printing plates. Plates should be at the press

site and checked against the copy to be

printed.

Ink. Ink should be at the press site and

checked for the proper color and quantity.

Stock. Stock should be at the press site and

checked against the work order for size,

flute and test. Board test refers to the prop-

er liner, medium weights of stock and flute.

Once the crew has determined that these

items are at press side and meet require-

ments, the press setup may begin. All safety

lockout devices must be in the proper posi-

tion before beginning the setup.

Set the Feed Mechanism

The press setup is initiated by the setup of

the feed mechanism. The basic height of the

feed table is fixed in relationship to the bot-

tom feed roll, the pull roll collars and the

print cylinder with the plates attached.

First, the side-hopper feed guides and

208 FLEXOGRAPHY: PRINCIPLES & PRACTICES

A print card layout

contains specific

instructions for the

job being printed,

including dimensions,

position, color, quantity

and in most cases,

a graphic layout of

the job.

Side guides are

mounted on a bar

across the feed table.

A back stop is set by

placing a stack of stock

within the feed guides

and adjusting to the

width of the blank.

backstops must be set. Many corrugated

presses set up over center, meaning that the

length of the sheet to be printed is in the cen-

ter of the press. The feed (side) guides are

mounted on a bar across the feed table and

have measurement tapes or scales attached.

They are adjustable on this bar from the cen-

ter of the machine to either side and are

locked by means of a screw-handle device.

Feed guides should be positioned on the

CUSTOMER

REMARKS

JOB#

BOX NO.

PLATES RECEIVED CUST

PLATES USED ON

REPLACES

NO.

LOCATION

COLORS

PANELS

TRANSPARENCY

PRINT CARD

GPB

PE PRP

MASTERS FOR DIES LOCATED AT

Side Guide

Backstop

guide bar one-half the stock length from cen-

ter (Figure ) .

The backstops must be properly posi-

tioned in conjunction with the feed hopper.

Proper setting of the backstops is best

attained by placing a stack of the stock to be

run within the feed guides and adjusting

according to the width of the blank, as seen

in Figure ). This setting will vary depend-

ing on the type of feed style being used, such

as a kicker feed or a lead-edge feed.

Set the Feed Gates

Feed gates should be set to allow only one

flute thickness of stock to pass under it during

the feeding operation of the press. If the feed-

er should allow more than one sheet to pass at

a time, the press may jam. It is important to set

the feed gates for each job to be run. Similar

grades of corrugated board may differ in

caliper due to variations in manufacturing.

All corrugated presses have two feed

gates (Figure ). Once each gate has been

set for proper caliper, they each should be

placed at an equal distance between the feed

guides (hopper) and the center of the press.

The feed gates are adjusted by sliding one

sheet of board under the gate and allowing an

additional space the thickness of one-quarter

of the caliper of the board (Figure ) .

When working with a press that has a com-

puter control system, the setting should be

checked with a sheet of board and fine tuned

before the run.

Set the Feed Device

The two most common feed devices used

on direct-print presses are the kick feeder

and the lead-edge feeder. The kick-style

feeder hits the sheet from the rear edge to

push the board into the press. The lead-edge

feeder carries the sheet into the press from

the front edge of the sheet.

To adjust a kick feeder, the operator

should set the kicker bar to the width of the

board being run (Figure )

To adjust a lead-edge feeder, the operator

typically only sets the feed gates and feed

guides because the feed action is preset for

PRESSROOM PRACTICES 209

Feed gates should be

set so as to allow only

one board to pass onto

the press at a time.

Feed gates are raised

or lowered by rotating

the dial at the top.

The feed gates are

adjusted by sliding

one sheet of board

under the gate and

allowing an additional

space the thickness of

one-quarter of the

caliper of the board.

210 FLEXOGRAPHY: PRINCIPLES & PRACTICES

most operating conditions (Figure ) .

The next step in the setup of the feeding

device is to set the feed roll. On manually set

machines, the feed roll is set with a locking

lever adjustment. The feed roll has an up and

down adjustment. It must be set tight

enough to grip the blank so as to prevent

slippage as the blank enters the press

(F i g u r e ). More feed-roll pressure is

required on prescored blanks than on non-

prescored blanks to prevent score-line slip-

page of the blank when it is entering the nip

of the rolls. Score-line slippage can cause

print and slot variation. On many newer

presses, the feed-roll setting is done with a

computer using motorized methods.

All feed sections have a caliper setting

adjustment, which consists of a handle that

raises and lowers the rolls. The caliper set-

ting should be set to the caliper of the board

being run. Often, the caliper readings on the

presses are approximate due to feed-roll

wear or play in the gear mechanism. If this is

the case, the machine should be recalibrated

to eliminate error and board crush.

Check Plates to Print Card

After the press-feed section has been set,

and before the plates are mounted in the

press, the plates should be checked against

the print card to verify that the copy is cor-

rect for the job to be run. Once the copy has

been verified, the plates should be checked

for damage, ink and wax buildup, dirt from

previous runs and proper bonding to the car-

rier sheet.

Select the Print Stations

Before the plates are mounted to the print-

ing cylinder, the operator must determine

which print station to use for each color.

When selecting the print station, considera-

tion should be given to how the graphics

must be trapped. The graphics are usually

prepared on the plates to have the ink colors

printing from lightest to darkest, allowing the

darkest ink color to trap the lightest in areas

where there is registration between colors.

The subsequent colors hide the lighter color

beneath it to create good trapping.

Mounting the Plates

to the Print Cylinders

Plates should be mounted on the appropri-

ate plate cylinders after a decision has been

made about which station to use for each

color based on the trapping requirements of

the graphics.

There are various methods used to mount

the plates on corrugated presses. The fol-

lowing three methods are typically used:

• In F i g u r e , individual plates are

mounted onto the plate cylinders using

scribe lines that are engraved on the

A lead-edge feeder

transports the board to

the press by grabbing

it from the lead, or

front edges.

Feed rolls must be set

tight enough to grip the

blank so as to prevent

slippage as the blank

enters the press.

cylinder. Scribe lines on the plate cylin-

der are also used to position plates that

are premounted on a carrier that has a

center mark. The center mark on the car-

rier is positioned to a cylinder’s center

scribe line and adhered.

• The plate cylinder is magnetized and the

plates either have a metal backing or are

positioned on a metal carrier. The mag-

netism of the plate cylinder holds the

plates in position without the use of tape

or straps.

• The plate cylinder uses a clamping system

to hold the mounted plates. The plates are

premounted on a carrier that has a

hooked lead edge. This edge is attached to

a bar and clamp mechanism on the lead

edge of the plate cylinder. The trailing

edge of the carrier is then attached to the

plate cylinder with straps, clamps or tape

(Figure ).

Set the Pull Rolls

The purpose of pull rolls is to control the

movement of the sheet from one print sta-

tion to the next without slippage or change

in board speed. These rolls control the print-

to-board register throughout the press.

The operator can set the pull rolls either

manually or with a motorized system. The pull

rolls are set in a position to ride on the ends of

the sheet and away from any printed copy.

Running pull roll collars over the printed

image may cause ink smearing on the board.

Set the Ink Distribution System

The ink distribution system should be set

up to maintain a constant, uniform supply

of ink during the pressrun (Figure ).

Ink the Print Stations

The next step in the setup procedure is to

ink up the print stations. The following pro-

cedure details a typical print station inking:

1. Double-check the color in the ink con-

tainer to verify that it is the color to be

placed in that print station.

2. Circulate the ink in the ink pump

through the supply hose back into the

pump to remove air from the system.

3. If an ink pan is being used, align the ink

pan and lock down the hold-down

mechanism. Ensure that the pan will

not rub on the ends of any rolls or the

surface of the plate cylinder.

4. Connect the return hoses from the ink

pan to the ink pump, making sure they

are routed around any moving parts. If

using submersible pumps, return hoses

must be slightly submerged in the ink

of the ink-pumping unit to help avoid

foaming with water-based inks.

PRESSROOM PRACTICES 211

Scribe lines engraved

on the cylinder

facilitate positioning

of the plate during

mounting.

In this mounting

system, a hooked edge

on the plate carrier is

fitted to a clamp on

the cylinder to provide

a strong fit. A clamp

at the trail end of the

carrier sheet provides

additional support.

Tension Clamp

Carrier

Sheet

Printing

Plate

Leading Edge

212 FLEXOGRAPHY: PRINCIPLES & PRACTICES

5. Connect the supply hose from the

pump to the ink-distribution system.

6. Pump the ink into the distribution sys-

tem.

7. After the ink has been pumping for a

time, check the pH and viscosity. These

measurements are done to ensure that

the ink is at its running parameters be-

fore the pressrun begins. If the ink does

not meet specifications, it should be

adjusted and rechecked until it does.

Set the Fountain Roll

and/or Doctor Blade

Once the ink is in the fountain and is with-

in its recommended running pH and viscosi-

ty parameters, the anilox roll may be inked.

When using a two roll system (Figure ),

the fountain roll is adjusted to squeeze against

the anilox roll. Once the press is started, the

rubber roll is adjusted to evenly squeeze the

ink off the anilox using the minimum amount

of pressure. This pressure setting is checked

by backing the fountain roll off until the oper-

ator can see the nip flood with ink. Then the

operator squeezes back in with both sides of

the rubber roll, making sure they are even,

until the flooding on the surface goes away. By

doing this several times, the ink wipe is set.

When setting a station with a doctor blade

(Figure ), the doctor-blade assembly is

set into its holder and then slowly tightened

down until it touches the anilox. As the blade

is tightened to the anilox, the operator will

notice that the ink will meter from the center

of the anilox roll outward to the ends. When

An ink distribution

system should be

configured to maintain

a constant, uniform

supply of ink during

the pressrun.

Anilox Roll

WiperRoll

Ink Pan

Filter

Air

Supply

Ink

Bucket

Pump

Return

the ink is metered off of the ends of the

anilox roll, the wipe is set. Similar to the pro-

cedure for setting fountain roll pressure, the

doctor blade should be backed out and

brought back in to the anilox several times in

order to set the wipe with the minimum

amount of pressure. Overtightening the doc-

tor blade can cause the blade to fold under

the pressure, causing the ink to dry due to

the friction and heat buildup behind the

blade. If ink drying occurs, the dried ink pig-

ments can cause damage to the anilox roll.

If the press is equipped with a cham-

bered doctor-blade assembly (Figure ),

the assembly is installed before the pump

is turned on. The ink wipe should be set in

the same manner as a single blade.

Adjust Print Impression

Print impression is measured in thou-

sandths of an inch with a micrometer. The

amount of pressure needed to transfer ink

to the surface of the board is dependent

upon the following:

• printing plate caliper;

• substrate porosity;

• board grade;

• ink transfer characteristics; and

• substrate texture.

On some presses, the impression setting is

adjusted automatically by means of comput-

erized controls. The computer may be pro-

grammed for settings of various board

calipers. On other presses, the operator must

manually set the impression by following

scales for the approximate setting. In either

case, the operator must fine-tune the setting

to achieve the minimal pressure needed to

transfer ink.

Print impression should be set as light as

possible since excessive impression will

crush the board’s flutes and cause box com-

pression-strength failure. Excessive impres-

sion may also cause fine print to distort and

reverses to fill in. The actual impression

needed on a board is determined by running

boards through the press at run speed

instead of jog speed. A portion of a board is

PRESSROOM PRACTICES 213

In a two-roll system,

the fountain roll should

contact the anilox with

the minimum amount

of pressure necessary

to evenly squeeze ink

off the anilox.

When using a doctor-

blade assembly,

the blade should be

placed in its holder,

then slowly tightened

until it touches the

anilox.

A chambered doctor-

blade system must be

installed before the ink

pump is turned on.

Impression

Cylinder

Sheet Travel

Plate

Cylinder

Printing

Plate

Feed

Rolls

Pull

Rolls

Reverse Angle

Doctor Blade

Anilox

Roll

Ink Nip

Impression

Cylinder

Sheet Travel

Plate

Cylinder

Printing

Plate

Feed

Rolls

Pull

Rolls

Wiper

Roll

Anilox

Roll

Ink Nip

Anilox Roll

Reservoir

Ink “Out”

Return

Ink “In”

Supply

Containing

Doctor Blade

Metering

Doctor Blade

214 FLEXOGRAPHY: PRINCIPLES & PRACTICES

bases to reach the color standard. All of the

information from the color-matching process

should be documented so the job can be

reprinted without additional downtime.

Press Setup Checklist

Before the pressrun begins, most com-

panies require that a press setup checklist

be filled out. A checklist ensures that all

the details of the job setup are covered

and documented for any future runs.

Information on the checklist may include:

• ink pH and viscosity;

• print location;

• ink color;

• stock;

• copy accuracy;

• feed-roll impression;

• print impression;

• pull-roll impression;

• print clarity;

• plate condition; and

• anilox configuration.

Setup time is expensive, especially when

it must be redone. Proper setups and con-

stant verification of the product during the

pressrun saves time and money.

PRESSRUN PROCEDURES

The attention to detail that marked the

setup process must carry over into the

pressrun. The next section describes main-

tenance that takes place once the press is

running.

Monitor Ink pH and Viscosity

In order to maintain the ink’s color-to-stan-

dard match throughout the pressrun, pH and

viscosity must be monitored. Without moni-

toring, the color will vary, resulting in incon-

sistent product. Ink pH and viscosity must

also be monitored to ensure proper trapping

between colors, good ink resolubility, good

print quality and correct ink drying between

cut out, calipered and saved in order to mea-

sure feed roll crush. The remainder of the

board is fed through the press. The thickness

of the unprinted area of the board is mea-

sured and compared to the saved piece to

determine any difference in caliper. Correct

print pressure is checked by comparing the

caliper of the printed area to the caliper of

the unprinted area. Once the feed-roll pres-

sure and print-impression pressure is adjust-

ed, the printed images are registered to the

board and to the other colors.

Check Colors to Standard

Once the press is set up and all settings are

complete, the printing must be checked for

accuracy against the color standard that was

approved by the customer in the design

stage of the job. A color standard may be an

ink sample on the board being printed, a

GCMI color chip or a printed sample from a

previous run.

All visual color-matching should take

place in a viewing booth designed for this

purpose. This type of booth provides a stan-

dardized light source with a neutral gray

background to eliminate color variations

caused by the lighting conditions during the

color-matching process.

A sample of the print should be compared

to the color standard to ensure that the print-

ed job meets the customer’s requirements.

The operator should check to make sure the

color is printing at the correct density (light-

ness and darkness) either visually or with the

use of a densitometer. If the color is not print-

ing at the correct density, the anilox may be

changed to achieve a density match with the

standard. For slight density changes that are

needed, the ink viscosity may be changed by

adding water, or the ink may be extended to

reach the color standard.

The ink hue should also be checked visu-

ally in a light booth or with the aid of a spec-

trophotometer. If changes in hue are needed,

the operator should add the correct ink

print stations, especially if the press does

not have between-station dryers.

Water-based inks should be run in a spe-

cific pH range to keep them working effi-

ciently. The pH ranges vary by ink manu-

facturer and the requirements for the job.

Generally, water-based inks are in the pH

range of 8.0 to 9.3. When the pH of a water-

based ink falls too low, the ink will begin

to body and thicken, eventually causing

rewetting problems and dirty printing. If

the pH is too high, the viscosity of the ink

will be too low, causing drying problems.

Color variations and print defects caused

by pH levels can be eliminated by main-

taining pH within its recommended range.

A pH meter is the instrument used to

read pH levels (Figure ). These instru-

ments should be calibrated to a buffer solu-

tion with a known pH on a regular basis.

To help control drying and to provide bet-

ter trapping between colors, the pH value

should decrease slightly from print station

to print station, starting from the ink station

closest to the in-feed and going to the out-

feed section. Because the pH level controls

the drying of water-based inks, this pH

decrease helps the ink to dry properly

before the next ink-down hits the board,

providing better trapping between colors.

Because the pH level of water-based inks

controls overall ink performance, pH should

always be checked before viscosity. Adjust-

ments made to viscosity alone may also

change the pH, causing other print prob-

lems. The pH and viscosity of water-based

inks should be checked every 30 minutes

(Figure ).

Water and amine are used to control vis-

cosity in water-based ink systems. A stabiliz-

ing varnish may also be used, which is a water

and amine combination that has been pre-

mixed to the correct percentages for the ink

system being used. An addition of stabilizing

varnish should lower the ink viscosity while

maintaining the pH of the ink. Water alone

will reduce the viscosity, but it may also

reduce pH, and cause other print problems.

Ink reducers may also be used to control vis-

cosity. Adding small amounts of reducer

should maintain correct viscosity. The viscos-

ity level should never get so high that more

than a pint of reducer is required to return the

viscosity to the correct level. The careful con-

trol of pH and viscosity levels for water-based

ink results in consistent color and uniform

ink flow throughout the production run.

Adding Ink to the Fountain

During longer runs, the press operator

may be required to add ink to the fountain or

pump. This addition requires specific atten-

tion to detail. The following text details a

typical ink addition procedure:

PRESSROOM PRACTICES 215

During the pressrun,

pH can be quickly

checked through the

use of a pH meter.

One method of

checking viscosity

is by timing ink flow

through a Zahn cup.