FTA (изд-во). Flexography: Principles And Practices. Vol.1-6

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186 FLEXOGRAPHY: PRINCIPLES & PRACTICES

based inks), or pH and viscosity (water-

based inks), must be maintained.

When doctor blades or chamber blade sys-

tems are used, high viscosity inks will cause

ink starvation by not reloading the anilox

cells. The print will not be consistent and the

color variations in the product will not be

acceptable to the customer. If the ink is run-

ning at a lower viscosity than the viscosity of

the color match, the color will get lighter. If

the viscosity gets too close to the minimum

running viscosity for that ink, printing

defects may occur.

Controlling Ink Viscosity and pH. Viscosity

checks should be completed every 10 to 15

minutes when using solvent-based inks.

When using water-based inks, pH and vis-

cosity should be checked every 30 minutes.

It is important to check pH first, followed by

viscosity, when using water-based inks

because the viscosity is affected by the pH

level. Solvent inks require more frequent

A checklist approval

form ensures that all

areas of setup have

been carried out

properly.

SUPERVISOROPERATOR

I HAVE MADE ALL THE APPLICABLE CHECKS AND APPROVE THIS ORDER FOR START-UP.

COMMENTS:

BOXES

LABELING

STANDARD

OPERATION

INK

SPECIAL SIZE

SPECIAL

REWINDER

SHRINKWRAPPING

SHIPPING FROM PRESS

FANFOLDING

PADDING

TRIMMER

OTHER

TIPPING

WRITE ON

PRIMER

FACE COPY—WATER BASED

FACE COPY—SOLvENT BASED

BACK COPY—WATER BASED

BACK COPY—SOLVENT BASED

COPY REGISTRATION REWIND

READ

QUALITY LEVEL

COLOR SEPARATIONS

IMPRESSION

NO SPLICES SIZE OF FOLD

PINFEED HOLE ALIGNMENT

UV CURING

VARNISH

TAPE TEST RUB TEST

LIST PMS COLORS

POSITION

QUALITY

MISC. MACHINE COUNT:

% OVERRUN

FANFOLD FOLDING STRAIGHT

CUTTING CLEAN

POSITION OF FOLD

PERF TEARS CORRECTLY (NOT TOO HARD/NOT TOO EASY)

HINGE FOLDING CORRECTLY

SPLICES REQUIRED

DIE CUTS HAND APPLIED

REGISTRATION

PERFED

CUTTING CLEAN

SINGLES LAY FLAT

MACHINE APPLIED

DIE CUT

SCORED

LINER TEST

JOG EVEN SIZE

MULTIWEB

OR COUPON

CONSTRUCTION TYPE

BASE STOCK

PROPER RELEASE (NOT TOO TIGHT/NOT TOO EASY)

GLUE

TOP STOCK

SIZE JACKET

MOCK-UP

DIE NO.

LINER SIZE

CARD CURL

BUTT CUT

SLITS

HOLES

SHEETED

MARGINAL PUNCHES

TEAR TAB

SCRATCH OFF

UPC SCAN

CUSTOMER

DATE

STOCK

JOB NO.

PRESS NO.

INV. NO.

PRESS APPROVAL START-UP SHEET

ITEM NO.

SIZE

checks of viscosity since the solvent evapo-

rates quickly and is more unstable than the

water in water-based inks.

To control an ink’s viscosity, small am-

ounts of a reducer should be added. The vis-

cosity level should never get so high that it

takes more than a pint of reducer to return the

viscosity to the correct level. Careful control

of ink viscosity (pH and viscosity for water

inks) results in consistent color and uniform

ink flow throughout the production run.

To control solvent-based ink viscosity, sol-

vent reducer is added during the pressrun.

The make-up solvent should have a slightly

higher percentage of the fast solvent than the

solvent in the ink system. For example, if the

ink system is 10% normal propyl acetate and

90% normal propyl alcohol, the acetate is the

fast solvent and will tend to evaporate faster

than the alcohol, which is the slow solvent in

the blend. The make-up solvent should be a

slightly higher concentration of acetate to

keep the ink stable, as well as maintain the

viscosity during longer runs.

To control viscosity in water-based ink sys-

tems, water and amine are used. A stabilizing

varnish may also be used. Stabilizing varnish

is water and amine that have been premixed

to the correct percentages for the ink system

being used. An addition of stabilizing varnish

should lower the ink viscosity while maintain-

ing the pH of the ink. Water alone will reduce

the viscosity, but it may also reduce pH, which

causes other print problems.

Many presses that are used for long runs are

equipped with automatic viscosity controllers.

Viscosity controllers dispense a predeter-

mined amount of solvent into the ink system

to keep the ink stable throughout the press-

run. It is important, however, to check the vis-

cosity manually when using these controllers

to ensure that they are working properly.

Water-based inks should be run in a specific

pH range to keep them working efficiently.

The pH range for a given ink varies by manu-

facturer and the requirements of 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 rewet-

ting problems and dirty printing. If the pH is

too high, the viscosity of the ink will be too

low, causing drying or blocking problems.

Color variations and print defects caused by

pH levels can be eliminated by maintaining pH

within its recommended range.

A pH meter is the instrument used to read

pH levels. These instruments should be cali-

brated to a buffer solution with a known pH

on a regular basis. Similar to viscosity con-

trollers, many presses have automatic pH

controllers that check pH and add predeter-

mined amounts of stabilizer or amine to main-

tain the proper pH level in the ink. Operators

should double-check these devices by read-

ing the pH manually to guarantee they are

working properly during the run.

Adding Ink to the Fountain

During longer runs, the press operator may

find more ink is needed. This requires specif-

ic attention to detail. The text below details a

typical ink addition procedure:

1. Double-check the ink to be added for

correct color. Do not assume that an

ink container is marked correctly.

2. Adjust viscosity (and pH for water-

based inks), of the ink to be added.

Solvent-based ink to be added to the

fountain should be thinned to a vis-

cosity that is two to four seconds high-

er than the ink in the fountain.

Viscosity of water-based inks should

be five to 10 seconds higher than the

ink in the fountain. Agitation of the ink

will cause a viscosity drop of three to

five seconds.

3. Add only enough ink to bring the level

back to the optimum level.

The optimum level should be determined

before the production run. It is based on the

PRESSROOM PRACTICES 187

188 FLEXOGRAPHY: PRINCIPLES & PRACTICES

amount of ink coverage for a given color,

which depends on the ink coverage for the

job being printed. The big print areas that use

more ink will require the ink pans to be filled

more often than those that use little ink. Add

fresh ink each hour to a low coverage area

rather than filling up the fountain and adding

only solvent or stabilizer for the whole shift.

Fresh ink helps maintain the correct balance

between colorant, resin and solvent (water

and amine for water-based inks).

Ink loses printability and flow characteris-

tics if only solvent (water and amine for

water-based inks) is added over a period of

time. This loss is due to the depletion of the

colorant and the resin in the ink. For the ink

to work properly, and to avoid printability

problems, press operators must know the

following about the inks they are using:

• upper and lower working viscosity

limits;

• solvents and additives to be used;

• range of pH for water inks; and

• maximum pigment load the ink can

handle.

By maintaining the proper percentages of

ink components, the color will be more con-

sistent and fewer print problems will occur.

Inspection and Quality Checks

During a pressrun, the operator should

make ongoing inspections of the press and

the job being printed. The following items

are typical pressrun checks:

• Listen to the press for any unusual noises

that may indicate a mechanical problem.

• Double-check the ink level in the foun-

tain or pumping unit. When using a

pump, check the ink flow to the pan.

• Ensure that the low roll indicator is on.

Prepare for roll changes and splices.

• Monitor print quality during the press-

run with the use of a strobe light, video

monitor or the naked eye.

During the pressrun, print registration

may change. This change in registration

could be due to any of the following:

• incorrect web tension between in-feed

and out-feed ends of the press;

• rewind roll tension is too high;

• web splices offsetting the web;

• rolls of stock varying from roll to roll;

• baggy edges on the rolls of stock mov-

ing the web to one side; and

• web thickness and adhesive coating

vary on rolls.

Inspecting a print sample is the most accu-

rate check of print quality. Operators should

not rely on checking print quality on the

moving web alone. Samples of the printed

product must be checked visually with the

aid of a magnifier for poor registration, poor

ink lay, color drifts, color match and ink

adhesion or cure (Figure ).

During the inspection the operator should

be looking for variations in:

• the cleanliness and sharpness of the

print;

• ink or impression misses;

• ink picking;

• flaws due to plate lift, lint or other

causes; and

• print quality.

Printed samples should be checked against

A magnifier, or loupe,

should be used to aid

in visual print checks.

the color standard on an ongoing basis to

ensure consistency throughout the run. If a

densitometer or spectrophotometer is being

used when the job is set up, and during the

initial color match, it should be used during

the pressrun. Samples from each printed roll

should be evaluated.

Color-drift checks are performed by laying

consecutive samples in a row on a white

background (Figure ).

Ink-adhesion tests are performed by put-

ting cellophane tape firmly onto the printed

image and pulling upward from the image

slowly for half of the length of the tape. The

remaining tape is pulled quickly off the other

half. The tape is then examined to see if it is

free of ink (Figure ).

Rewind tension must be monitored regular-

ly. Too much or too little tension will cause the

roll to telescope or collapse. Variances in the

tension may also cause registration or block-

ing problems. Blocking occurs when the ink

or varnish sticks to the back of the liner.

Die-cutting and stripping quality must be

checked throughout the pressrun to ensure

consistency from label to label and roll to roll.

One cause of die-cutting changes during a run

is heating of the die and the anvil roll. As a

result, the running pressure between these

two rolls increases. The operator must make

periodic adjustments to offset that change.

Quality Awareness

The flexographic printing process requires

consistent and careful monitoring during the

pressrun. There are no assurances that a job

printing well presently will be doing so in five

or 10 minutes. Proper pressrun procedures

are the mainstream of top quality finished

products. Press operators must learn and per-

form all pressrun procedures well. Quality

checks should be performed regularly and the

results should be documented. These results

should be kept for a period no less than the

life of the product produced. Quality is the

result of conscious effort by the operator.

Shipping Preparation

Shipping specifications are typically on

the job jacket for each printing order. The

product labels should be checked closely.

Personnel must ensure that the customer is

provided the proper information for weight,

footage, number of impressions or a combi-

nation of these items. Some customers may

also require densitometer or spectropho-

tometer readings from the finished rolls.

Preparing for the Next Job

Preparing for an upcoming job is com-

monly done while the current job is running.

Preparation generally requires assembly of

the necessary plate rolls, substrates, inks,

cores and tooling. The press operator and

assistants should perform the following

PRESSROOM PRACTICES 189

Check for color-drift of

the printed piece by

laying consecutive

samples in a row on a

white background.

Testing for ink-adhe-

sion requires putting a

strip of cellophane tape

firmly onto the printed

image and pulling

upward from the image

slowly for half of the

length of the tape. Then

pull the remaining tape

quickly off the other

half. The tape is exam-

ined; it should be free

of ink.

190 FLEXOGRAPHY: PRINCIPLES & PRACTICES

activities in preparation for the next job:

• review information in the next

job jacket;

• plan print station wash-ups;

• note required inks and colors;

• note colors and anilox rolls in current

use that may be needed; and

• gather all materials and supplies.

CLEANUP PROCEDURES

Most jobs require some degree of cleanup

after a pressrun because inks for the next run

are often different. Since the press is prof-

itable only when it is in production, an effi-

cient cleanup program is needed. A correct

wash-up procedure minimizes downtime

between jobs and maintains the press in good

working condition. Cleanup procedures vary

by company and brand of equipment.

Before beginning the actual cleanup, the

operator should double-check the next order

to determine if any inks can remain for the

next job.

Cleanup Steps

The following details typical cleanup pro-

cedures:

1. Turn off all heaters and blowers so the

web is not damaged or burnt.

2. Remove all pressure from the dies, nip

rolls and fountain roll.

3. Remove the plate cylinder.

4. If using a pump, turn off the pump and

disconnect the power supply to stop the

flow of ink.

5. Remove the ink supply hose (if using a

pump).

6. Remove the stand pipe in the fountain

(if using a pump) and drain the ink back

into the ink container. Use a scraper or

card to push the remaining ink down

the drain hole.

7. If not using a pump, place the drain

hose from the fountain into the ink con-

tainer and remove the drain plug to

drain the ink. Use a card or scraper to

push the remaining ink down the drain

and into the container.

8. Plug the drain hole again.

9. Pull back on the doctor blade pressure

so it is not resting on the anilox.

10. Run the fountain roll into the anilox and

flood the rolls with cleanup solution.

11. Quickly remove the ink pan and doctor

blade assembly and place in a cleanup

container.

12. Clean the face and sides of the rubber

roll and anilox, and any other areas

where ink is built up, using a shop rag

and cleanup solution. Do not allow the

rolls to dry.

13. Wipe each roll with normal propyl alco-

hol to remove any residue from cleanup

soaps that may be used in a water-based

ink cleanup.

14. Clean the fountain pan and drain hose,

concentrating on areas where ink

buildup exists. Use a dry rag to give the

pan a final shine.

15. Clean the doctor blade assembly. Use

caution when cleaning the assembly.

Remove ink collected on all sides of the

assembly.

16. If using submersible pumps, place the

pump in a bucket of cleanup solution

and flush it out. This procedure cleans

the pump and the hoses. After flushing

with cleanup solution, flush with fresh

solvent or water.

17. Repeat the above steps for each print-

ing station.

18. Clean any excess ink or adhesive from

all impression cylinders, idlers and nip

rolls.

The print station of a two-roll system con-

tains pinch points between various rolls.

These pinch points are referred to as inward

nips (Figure ). Use extreme care in this

area because it is easy to catch a rag or fin-

ger in the nip.

Clean the Plates

The plates may be removed from the

plate cylinders for cleaning, or they may be

cleaned on the cylinders before demount-

ing. When cleaning solvent-based ink off of

the plates, the solvent blend for the ink sys-

tem should be used. Excessive amounts of

acetate should be avoided, as it will dam-

age the plates. When cleaning water-based

ink off plates, a cleanup soap should be

used (Figure ).

A soft-bristled brush may be used to scrub

the plate clean after the solvent or soap is

applied to the plate (Figure ). The plates

should be blotted dry with a rag or absorbent

towel. Avoid rubbing the plate as this may

damage the plate image.

Remove and Clean the Cutting Die

After the press stations and plates have

been cleaned, the die should be removed

and stored. Lay the die on a clean rag. A soft

fiber brush, wooden paint stick, or other

pointed instrument be used to remove any

adhesive or ink buildup in the areas between

the cavities of the raised engraving.

With the die cavities clean, the die should

be inspected for damage and stored back in

its shipping box or another protective stor-

age container.

Label Ink Containers

Ink containers used during the run should

be marked with the correct ink color and/or

number. Any additives, 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 disposal con-

tainer. The waste container should be recy-

cled 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

PRESSROOM PRACTICES 191

Pinch points between

various rolls are

referred to as inward

nips. The person clean-

ing the print station

must use extreme care

in this area because it is

easy to catch a rag or

finger in the nip.

A cleanup soap should

be used to remove

water-based inks from

the plate.

A soft-bristled brush

may be used to scrub

the plate clean after the

solvent or soap is

applied to the plate.

Impression

Cylinder

Substrate

Plate

Cylinder

Anilox Roll

Fountain

Roll

Nip Roll

Danger Zone

Nip Roll

Danger Zone

192 FLEXOGRAPHY: PRINCIPLES & PRACTICES

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 Ultraviolet Curing Units

When using ultraviolet (UV) curing sta-

tions for inks or varnishes, the curing unit

must be cleaned on a regular basis for it to

function properly and create the needed

radiation to set the ink or coating.

Use isopropyl alcohol to clean UV lamps

and reflectors. Cotton gloves supplied with

the lamp should be worn when installing or

handling the light source to keep skin oils

from coming into contact with the bulb. This

is important because oil from the skin will

affect the lamp’s performance.

etting up a wide-web press

varies from machine to machine.

This variation is due to the wide

variety of presses used in the

market today. For this reason,

this section focuses on the

basics of setup that are common to most

wide-web printers.

PRESS SETUP

The first step in press setup is to review the

job jacket (Figure ), job history sheet and

any supporting material such as prepress

proofs and previously printed samples of the

job. From this information, the press opera-

tor and press assistants must visualize how

the job must be set up to meet the customer's

requirements.

In many cases, a mounter proof is sup-

plied. This should be inspected to ensure

that the printing plates are not defective, reg-

istration between colors is correct, and

makeready is not needed on the print cylin-

ders to compensate for plate height varia-

tions.

Select the Print Stations

From the information contained in the job

jacket, mounter proof, and prepress proof or

sample, the operator must select the appro-

priate printing station for each print cylin-

der. A primary consideration when choosing

print stations is whether the job is a surface

print (design prints on the outside of the

substrate) or reverse print (design prints on

the inside of the substrate). For example, a

potato chip bag is surface printed to keep

the ink from coming into contact with the

chips; bathroom tissue is reverse printed so

that after packaging the ink will be against

the tissue to help protect the ink and

enhance the gloss of the package.

Surface-printed colors are placed in the

press so that the lightest colors are printed

first, and the darkest colors last. Reverse

print orders are just the opposite. This rever-

sal is to facilitate trapping the lighter colors

with the darker colors. All print stations may

not be required for a given job. The operator

must determine which stations to use based

on existing colors in the press, colors need-

ed for upcoming jobs, anilox rolls that are in

each printing station, and the drying capaci-

ty needed between print stations. Large ink

coverages may need to pass through several

between-deck dryers to dry the ink properly

before the next ink color is printed.

The print cylinders must be inspected for

damage to the plates, and to ensure that the

design on the plates matches the information

on the job jacket and supporting material.

Determine the Substrate Wind

Before cylinders can be shafted and

geared for the pressrun, it is essential to

determine the required unwind and rewind

for the job’s end use. A rewind number that

corresponds to the position of the copy on

the printed roll is assigned to the design

(Figure ). This rewind number deter-

mines the end of the plate cylinder on which

PRESSROOM PRACTICES 193

Wide-Web

Press Procedures

194 FLEXOGRAPHY: PRINCIPLES & PRACTICES

the gears must be placed to provide the cus-

tomer with the correct wind for end-use

applications. In some cases, gears are not

interchangeable and the correct gear posi-

tion is determined when the job is mounted.

In this case, the operator needs to check the

gear and rewind numbers.

Install Cylinder Hardware

After the gear side of the plate cylinders is

determined, the necessary plate-cylinder

hardware must be installed in the correct

sequence. At this point in the setup

sequence, the operator or assistant should

place the bearers, gears, bushing and regis-

ter control mechanisms on the plate cylin-

ders. Some cylinder hardware setup should

be performed during the previous pressrun

to help reduce downtime.

Change Anilox Rolls

In many cases, anilox rolls must be

SHIPPING

OTHER OPERATIONS

PRESSROOM

PLATEROOM

STOCK

JOB JACKET

SAMPLES TO:

PACKING SLIP

SHIP VIA:

BILL/LADING

OLS

REGULAR

PLAIN

OTHER

SPECIAL INSTRUCTIONS:

SHIP TO:

NEXT DAY 2ND DAY

REWINDING

BURSTING

TRIMMING

COLLECT

OTHERSHIP FROM:

PREPAID

OLS

COD

SPECIAL INSTRUCTIONS:

CARRIER

AMOUNT PER ROLL

FINISHED SIZE

CORE SIZE

CYLINDER SIZE

NO. ACROSS

NO. AROUND

DIE SPECS

GRAPHICS SPECS

MARG. LEFT

MARG. RIGHT

HORZ.

VERT.

PERFS:

FANFOLD ATPINFEED:

NO. PER SHEET

REWIND

POSITION

HORZ.

VERT.

SLITS:

DIE NO(S)

PERF/SHEETER

PRINT CYL(S).SIZE

ORDERED

REC'D

SPACING

CYLINDER SIZE

NO. ACROSS

NO. AROUND

SPACING

DATE SENT

CARTON SIZEOTHER

AMOUNT PER PACKAGE

SPECIAL INSTRUCTIONS:

AMT. PER CTN.

INITIALS

PLAINOLSSHIPPING LABEL

SHRINKWRAPPING

FLEXO

LEFT RIGHT

LETTERPRESS

SAME

MACHINEHAND

BUTT CUTDIE CUT

SHEETEDOTHERCARRIERCARDLABEL

FRONT

ROLLS

CONTINUOUS

SIZE ACROSS

CORNER RADIUS

CUSTOMER NO.

CUSTOMER

DESCRIPTION

REQUESTED SHIP DATE

RUSH NO.

SALES PERSON

PREP’D BY

ACTUAL SHIP DATE % OVERRUN % UNDERRUN

QUOTE NO.

PO NO.

REPEAT NO.

DATE ORDERED

JOB NO.

TOTAL QTY.

PRESS NO.

10)

BACK

AROUND

PRESS DRAW

LINER SIZE

COLORS

NO. OF NEW PLATES

HERE

VARNISH: OVERALL SPOT

SPECIAL INSTRUCTIONS:

YESOVERLAMINATE NO

NO. OF REMARKS MADE BY MOUNTED BY

JOB NO.

A job jacket is a

folder or envelope

that stores valuable

information about

the job to be run.

PRESSROOM PRACTICES 195

A rewind number

corresponds to the

position of the copy

on the printed roll.

The rewind number is

used to determine the

unwind and rewind

requirements for the

job.

changed in the press during the setup of a

job to acheive the correct ink density for the

design. Changing anilox rolls is often more

complicated than changing plate cylinders

since more disassembly of the press is

required. An anilox that is removed or

installed in a print station should be covered

to protect against surface damage.

Anilox Roll Selection Guidelines

Anilox roll selection varies with the print-

ing application, substrate, plate material and

the ink system being used. The best selec-

tion is an anilox roll that will provide the ink

transfer needed to meet the customer’s color

standard while providing consistent inking

of the images on the plates. This selection

rule is especially true when printing tone or

process work.

When selecting laser-engraved anilox rolls,

consider the following general guidelines:

• 60° engravings are generally used for

most applications. Although laser en-

graved anilox rolls can be manufactured

with 30°and 45° configurations, 60° rolls

have been shown to provide advantages

in ink release.

• Line-count selection is determined by

the copy to be reproduced on the press.

In applying coatings and varnishes, rolls

with line counts of between 85 and 200

are commonly used. For printing solids

(large ink coverage areas), line counts

of between 200 and 400 are usually used.

When printing screened areas (tone and

process images), the general rule is to

use an anilox roll with a minimum of a

4:1 ratio between the line count of the

screened area on the plates and the line

count of the anilox roll. In other words,

to print a 100-line process job, an anilox

with a minimum of 400 lines should be

selected. In this example, the higher

line-count roll can be used to provide

finer inking of the plate images as long

as the density of the print can meet the

color standards for the job. This 4:1 ratio

is only a general starting point.

• Cell-volume selection is determined by

the job to be produced on the press. A

volume range of 1.6 BCM (billion cubic

microns) to 4 BCM is generally used for

reproducing screen and process work.

Rolls with a BCM between 3 and 7

should be selected for printing line

work. Volumes used for printing solids

are generally in the 5 to 8 BCM range.

Higher BCM rolls should be used to

apply coatings, adhesives and varnishes.

Load Cylinders into

the Print Stations

After the anilox rolls have been selected

for the job and are loaded into the press, the

print cylinders should be loaded into the

Printing

Reads

This Way

rin

tin

Printing

Reads

This Way

rin

tin

Printing

Reads

This Way

rin

tin

Printing

Reads

This Way

rin

tin

1. 2.

3. 4.

5. 6.

7. 8.