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

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216 FLEXOGRAPHY: PRINCIPLES & PRACTICES

1. Double-check the ink to be added for

correct color. Do not assume that an

ink container is marked correctly.

2. Adjust pH and viscosity of the ink to

be added. Viscosity of water-based

inks should be five to 10 seconds high-

er than the ink in the fountain. Agita-

tion 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

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, water and amine.

Ink loses printability and flow characteris-

tics if only water and amine are added over a

period of time. This loss is due to the deple-

tion 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 use;

• range of pH for water inks; and

• the 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.

Checking Quality

Conducting quality checks during a press-

run is an important part of the printing oper-

ation. Once a job is set up and running, cer-

tain steps must be followed in order to main-

tain quality throughout the run.

Color Consistency. Visual color checks of

printed samples should be done using a light

booth in the same manner as the color check

of the setup operation. More and more instru-

mentation is being used to verify color con-

sistency. Specific tools such as densitome-

ters, colorimeters and spectrophotometers

have replaced simple visual color checks.

A minimum of one sheet every 15 minutes

should be inspected during the pressrun for

any variation in color away from the color

standard. The sheet should also be inspect-

ed for other defects that would affect the

final product.

Samples should be compared throughout

the run to ensure that there are no color

drifts. A color drift occurs when the color

shifts in successive production samples.

Color drifts are checked by laying consecu-

tive samples on a white background in a

fanned out arrangement. One of the most

common causes of color drift is substrate

variation. Samples should be cut for com-

parison, rather than folded or overlapped, to

allow for more accurate comparisons.

Inspections 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.

• Monitor print quality during the press-

run.

Inspecting a print sample is the most accu-

rate check of print quality. Operators should

not rely on checking print quality on the

moving sheet alone. Samples of the printed

product must be checked visually with the

aid of a magnifier for poor registration, poor

ink lay, color drifts and color match.

During the inspection, the operator

should look for defects and variations in:

• print registration (Figure );

• cleanliness and sharpness of print;

• ink or impression misses;

• ink picking;

• flaws caused by plate lift, lint or other

causes;

• print quality;

• board defects;

• tracking;

• fill-in;

• excessive pressures; and

• print-to-cut registration.

General Housekeeping

When the press crew is not tending to other

duties, general housekeeping work is always

needed around the press. A conscientious

operator and crew ensures that the work area

is kept clean and in a workable condition.

The operator should also be conscientious

about maintaining the machine. Any irregu-

larities in the press such as strange noises, oil

leaks or other unusual signs may signal an

impending breakdown and should be investi-

gated immediately. The operator should

ensure that all lockout and tag-out proce-

dures are followed when housekeeping is

performed inside the press.

Production personnel should pay attention

during the pressrun to make sure that all con-

sumables are available in sufficient quanti-

ties. Stock and ink should be monitored in

order to keep a steady supply available. It is

important that the machine is not shut down

due to a lack of these items.

Other items such as ink additives, rags, load

tags, reports and machine logs should be mon-

itored and replaced before they run out.

Prepare for the Next Job

Operators should begin the setup for the

next job during the current pressrun. Work

completed in advance of the changeover

allows for a smoother and more efficient

setup. The operator should review the up-

coming job order and plan the best and

fastest way to change over to the next job.

Production personnel can find problems and

solve them before the next setup begins by

checking all the materials before the next set

up.

Stock for the next job should be located and

inspected to be certain it is the proper stock,

the correct size, and is in good condition. The

stock grade, test and flute should be inspected

to ensure that it is correct. Variations should

be reported before the set up begins.

The ink required for the next job should be

located and inspected to ensure that it is the

correct formula and available in sufficient

quantities. Color standards should be re-

viewed to help determine print station selec-

tion and anilox roll requirements.

Tooling and plates for the upcoming job

should be checked prior to the setup to make

sure the tooling is available and the plates are

in good condition.

CLEANUP PROCEDURES

Most jobs require some degree of cleanup

upon the completion of a run. Inks for the next

run are often different, which requires that the

PRESSROOM PRACTICES 217

A loupe, or magnifier,

will be of great

assistance in print

inspection.

218 FLEXOGRAPHY: PRINCIPLES & PRACTICES

press equipment be washed. Since the press is

profitable only when it is in production, an

efficient 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.

When a color change is required for the

next run, the old ink must be washed out of

the machine and replaced with fresh ink of

the new color. Depending upon the direction

of the color change (from light to dark or dark

to light), the time required to do the wash-up

will vary. Without a thorough wash-up, dark

colors will contaminate the lighter ink colors.

Printing plates should be cleaned and

rinsed after a production run and prior to

being placed in storage.

Cleaning Equipment and Materials

Operators should ensure that all needed

cleanup equipment and materials are at the

press before the press goes down for cleanup.

It is important for the ink to be cleaned up as

soon as possible after the machine goes down

so that the water-based ink is more soluble

and can be washed up with water and a high

pH soap. Dried water-based ink is very diffi-

cult to remove.

The follow cleaning equipment and supplies

should be on hand:

• warm water (120° F);

• rubber gloves ;

• eye protection;

• clean rags;

• cleaning solutions;

• brass brush for chrome anilox rolls;

• stainless-steel brush for ceramic anilox

rolls;

• soft-bristled brush for plates; and

• coating material (such as vegetable

shortening) for corrosion protection on

weekend cleanups.

Opening the Machine

Upon completion of the run, the press is

opened for cleanup. Company lockout or

tag-out procedures must be followed when

working inside the machine.

Conserve Ink

In an effort to conserve ink, the ink pan is

often lowered and the liquid ink squeegeed

down the ink-return hose and back into the

ink pump before a wash-up begins. The return

hose is then switched to the wash-up contain-

er or drain and the wash-up process begins.

Manual Cleanup

The following procedure details a typical

manual cleanup after the ink has been

drained from the pan. Company procedures

may vary depending on the specifications of

the machine.

1. Turn off the ink pump and disconnect

the power supply to stop the ink flow.

2. Pump cleaning solution through the

entire system. This pumping makes the

entire system easier to clean.

3. Remove the ink supply hose from the

deck.

4. Stop the rotation of the rubber roll.

5. Release the pressure between the rub-

ber roll and the anilox roll.

6. Move the ink-return hose from the ink

pump to the wash-up container.

7. Reset pressure between the anilox and

rubber roll and restart their rotation.

8. Flood the anilox and rubber rolls with

wash-up solution as they slowly turn.

The solution will remove ink from the

surface of the rolls. Several passes

over the rolls with fresh solution may

be needed to throughly remove the ink.

9. Release the pressure between the

anilox roll and rubber rolls on one end

only.

10. Wipe the anilox roll. Begin on the side

with the released pressure. Use a fold-

ed rag or shop towel soaked with

cleaning solution. If water-based ink is

being washed up, it is best to keep the

fountain roll and anilox roll wet until

the ink is washed off. It is very difficult

to clean off water-based ink after it has

dried on the rolls.

11. When the end of the roll is reached, re-

lease the pressure on the remaining

end. Finish wiping the anilox roll.

12. Clean the rubber roll the same way as

the anilox roll.

13. Stop the rotation of the rubber roll and

thoroughly clean both ends of the

anilox and rubber roll.

14. Go over each roll with clean, warm

water to remove any soap residue from

cleaning water-based ink. The print sta-

tion of a two-roll system contains pinch

points between various rolls. These

pinch points are referred to as inward

nips (Figure ). The person cleaning

the print station must use extreme care

in this area, because it is easy to catch a

rag or finger in the nip.

15. Remove and clean the ink filter.

16. Reassemble the station.

Cleaning the Plates

Clean the plates with cleanup soap and

water to remove any dried ink. The plate

should be scrubbed with a soft-bristled

brush and cleanup solution. It should then

be blotted dry with a rag. Rubbing the plate

with a shop towel should be avoided, as it

can damage the plate surface. After the plate

is cleaned, it may be removed from the plate

cylinder. The operator should make note of

any plate damage or defect so that new

plates may be prepared for upcoming runs.

Chamber-bladed Station Cleanup

The following procedure details a typical

cleanup of a chamber-bladed system:

1. Disengage doctor-blade assembly from

anilox.

2. Lock the blade assembly into the

cleanup position using the appropriate

safety mechanism.

3. Clean the anilox roll by passing a fold-

ed clean rag, soaked in cleanup solu-

tion, along the entire face of the rotat-

ing roll.

4. Scrub the anilox with a brush. Use

brass bristles for chrome rolls, steel

for ceramic rolls.

5. Turn off the anilox drive motor and

wash both ends of the anilox thor-

oughly.

6. Remove any ink buildup off the sides

of the anilox.

7. Make a final pass with a clean damp

rag, followed by a clean dry rag.

Extreme caution is required when cleaning

the anilox roll when a doctor blade is being

used. The cleanup person must be aware of

the location of the blade to avoid accidentally

bumping it while cleaning. Doctor blades are

extremely sharp and can cause severe injury.

Doctor-blade Assembly Cleanup

Cleaning the doctor-blade assembly re-

quires direct contact with the doctor blade.

Cut-resistant gloves should be worn to mini-

mize the risk of injury. In some cases, the

blade assembly is removed from the press for

cleanup. The following procedure details a

typical cleanup for a doctor-blade assembly:

1. Soak a shop rag or towel in cleaning

PRESSROOM PRACTICES 219

The area between

two rolls is known as

the inward nip. When

cleaning, one should

be careful not to catch

a rag or finger in this

area.

Impression

Cylinder

Sheet

Travel

Plate

Cylinder

Anilox

Roll

Wiper

Roll

Nip Roll

Danger Zone

220 FLEXOGRAPHY: PRINCIPLES & PRACTICES

solution and wipe the inside and out-

side of the assembly. Also wipe both

sides of the blade. Light pressure will

reduce the chance of the blade cutting

through the rag.

2. Check the condition of the doctor

blade. Carefully remove blades that

show excessive wear or damage.

Properly dispose blades.

3. Continue cleaning the blade assembly

with a soaked rag until most of the ink

on the assembly is gone. Complete a

final pass with a clean damp rag to

remove any last traces of ink.

Ink Pan Cleanup

After washing the doctor-blade system, the

ink pan must be cleaned. The following pro-

cedure details a typical ink pan cleanup:

1. Put the pan into position for washing.

Scrape any liquid ink into the drain

hole.

2. Place a rag at the bottom of the ink pan

and saturate it with cleaning solution.

3. Pass the damp rag over the entire inte-

rior of the ink pan to rewet the dried

ink. 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.

Automatic Wash-ups

Automatic wash-up systems are built into

some machines. They have a fixed sequence

of operations that are done automatically

for the operator. The system may be used

during setup, between orders, or at the end

of a run or shift.

When the automatic wash-up system is

engaged, the ink is automatically drained

from the system into the ink bucket and

saved for future use. After the ink is drained

from the inking system, the press operator

removes the ink bucket from the platform.

Water or clean-up solution is then automati-

cally circulated, and often pressure sprayed,

throughout the entire system.

Water and ink residue is then removed

from the inking system automatically. The

residue is dumped into the plate waste

drainage system for treatment (Figure ).

Automatic wash-up systems basically per-

form the same steps listed in the section

describing manual wash-up of the ink sta-

tion. It is important to remember that auto-

matic wash-up systems do not scrub the

anilox roll, and therefore, do not eliminate

this cleanup step.

Mark Ink Containers

The containers holding the ink used during

the run should be marked with the correct

ink color or number. Any additives, bases or

solvents that were added to the ink, and their

quantities, should be noted on the contain-

ers. Container labels are often covered by ink

spilling down the side of the bucket. If a spill

Ink residue from an

automatic wash-up

system should be

dumped into the plate

waste drainage system

for treatment.

PRESSROOM PRACTICES 221

occurs, attach a new label or identify the

bucket in some other manner.

Weekly Cleanups

In some situations, the press may not

require a complete wash-up because the col-

ors being run from job to job are similar and

contamination is not a major problem. In

this case, some of the press components are

only cleaned thoroughly on a weekly basis.

At least once a week, following the normal

wash-up, the anilox roll should be scrubbed

with a brush made for this purpose.

Operators should remember to use a brass

brush for chrome rolls and a stainless-steel

brush for ceramic coated rolls.

The ink pan under the rolls should be

cleaned weekly. In many cases, the ink pan

is not removable, so the cleanup must be

done around the rolls and doctor-blade

assembly. It is common to coat the inside

and outside of the pan with a thin layer of

material (one that is approved by the ink

company) to keep ink from drying on the

metal. Vegetable shortening is often used.

Other machine parts and components

should be cleaned. Keeping the press and

press area clean not only maintains the

appearance of the plant, but leads to a

safer work place and a better press perfor-

mance record.

PADHESION, INK

BINDING

BLEED

1. Under color drying too slowly or over

color drying too fast.

2. Poor physical property resistance.

1. Improve under color drying rate by

reducing viscosity and/or ink film

thickness. Use a faster or slower sol-

vent as required. Adjust or check

between station dryers. (Preceding

colors must be dry enough to receive

subsequent colors laid down.)

2. Use proper ink formulation and pig-

ment grade selection.

■ An under color wet-

ting into an over

color in a trapping

or overprinting

application.

■ Diffused or migrat-

ing colors in a

dried/cured ink film.

1. Irregular web tensioning, substrate

moving independent of plate move-

ment.

2. Gear bottoming off pitch line.

3. Intermittent plate slur.

4. Excessive ink viscosity.

5. Noncompressible stickyback.

6. Low durometer plate materials.

1. Reduce web tension. Clean and lubri-

cate driven and undriven rollers.

Check web tensioning mechanisms

for proper operation.

2. See defect “Gear Marks.”

3. Run bearers.

4. Reduce ink viscosity.

5. Use cushioned stickyback.

6. Use higher durometer plate materials.

■ Intermittent dark

lines of varying

widths running in

the web direction of

printed image.

1. Improper ink

formulation/chemistry.

2. Insufficient heat and/or air volume in

main dryer.

3. Low treatment level of

substrate.

4. Excessively reduced ink viscosity,

binder destroyed.

5. Surface of substrate may be

contaminated.

6. Surface of substrate

may require special

application.

1. Check ink for correct type and grade

for substrate being run.

2. Increase heat and/or air volume in

main dryer.

3. Check surface of substrate for ade-

quate treatment level.

4. Restore and maintain ink viscosity at

optimum point.

5. Apply wash-coat prior to printing.

6. Apply primer prior to printing.

■ Ink fails to adhere

to substrate.

■ Fails tape test.

■ Fails crinkle test.

■ Fails rub test.

PRESSROOM PRACTICES 223

Appendix A

DEFECT/INDICATOR PROBABLE CAUSE CORRECTIVE ACTION

PRESSROOM TROUBLESHOOTING CHART

224 FLEXOGRAPHY: PRINCIPLES & PRACTICES

BLOCKING

BRITTLENESS

COLOR STRONG

COLOR VARIATIONS

COLOR WEAK

1. Excessive ink viscosity reduction.

2. Excess extender varnish.

3. Ink settled out.

4. Plugged anilox roll cells.

5. Incorrectly specified anilox roll.

6. Incorrectly specified fountain roll.

7. Tight setting of fountain roll nip.

8. Worn anilox roll.

1. Add fresh ink to restore viscosity.

2. Add pigment concentrate (toner).

3. Thoroughly mix ink in container

before adding to fountain.

4. Thoroughly clean anilox roll.

5. Select anilox roll with higher volume.

6. Select fountain roll with lower

durometer.

7. Decrease fountain roll nip pressure.

8. Replace/refurbish anilox roll.

■ Lacking color

strength and body.

1. Lack of viscosity and/or pH control.

2. Inconsistent press speeds.

3. Variation in ink batches.

4. Color contamination.

1. Maintain viscosity and/or pH control.

2. Maintain consistent press speed.

3. Mix adequate amount of ink.

4. Improve cleanup procedures.

■ Inconsistent color

throughout a press-

run.

1. Excessive ink viscosity.

2. Excessive pigment load.

3. Incorrectly specified anilox roll.

4. Incorrectly specified fountain roll.

5. Light setting of fountain roll nip.

6. Doctor blade incorrectly set.

1. Reduce ink viscosity.

2. Add extender.

3. Select anilox roll with lower cell vol-

ume.

4. Select fountain roll with higher

durometer.

5. Increase fountain roll nip pressure.

6. Adjust doctor blade to parallel with a

minimum pressure setting.

■ Excess ink transfer

to substrate.

■ Excess color

strength.

1. Excessive heat or UV exposure level

in drying/curing system causing a

release of moisture and plasticizer

from substrate or ink film.

1. Control web temperature. Reduce

heat and/or increase volume of air

through drying chamber. Reduce UV

lamp power.

■ Ink film/substrate

breaks or cracks

when flexed.

1. Improper ink drying.

2. Excessive pressure in rewind.

3. Excessive weight in stack.

4. Softening of pre-applied coatings.

5. Web rewound too warm.

6. Web rewound with excess surface

moisture.

1. See defect “Drying Too Slow.”

2. Reduce rewind tension.

3. Reduce stack height.

4. Use solvents that do not attack prior

coatings.

5. Reduce web temperature by chilling

within ±10° of room temperature or

reducing dryer temperature.

6. Avoid rewinding excess surface

moisture on web prior to rewind.

■ Undesired adhesion

between two

surfaces.

DEFECT/INDICATOR PROBABLE CAUSE CORRECTIVE ACTION

PRESSROOM TROUBLESHOOTING CHART

(CONT‘D)

PRESSROOM PRACTICES 225

CURING OF UV INK

BLOCKING

CURING OF, UV INK (INCIDENTAL)

DOT GAIN

1. Excessive ink volume.

2. Excessive plate thickness.

3. High density stickyback.

4. Low ink viscosity.

5. Excessive pressure settings.

6. Poor ink metering application.

7. Damaged or worn press components.

8. Dirt on impression and/or plate

cylinders.

1. Reduce anilox roll volume to a

minimum while maintaining color

requirements.

2. Use thinner plates.

3. Use cushioned stickyback.

4. Increase ink viscosity.

5. Reduce pressure settings to a mini-

mum.

6. Use bladed ink metering application.

7. Check and replace damaged or worn

gears, bearings or cylinders.

8. Clean impression and/or plate cylin-

ders.

■ An excessive

increase in the size

of a halftone dot

from film to the

printed image.

1. Direct exposure to sunlight.

2. Exposure to general lighting sources.

1. Eliminate direct sunlight exposure.

2. Use UV filter covers on general light-

ing sources directly over press.

■ Ink curing prior to

printing and UV

lamp exposure on

plates, rollers, etc.

1. Improper ink drying.

2. Excessive pressure in rewind.

3. Excessive weight in stack.

4. Softening of pre-applied coatings.

5. Web rewound too warm.

6. Web rewound with excess surface

moisture.

1. See defect “Drying Too Slow.”

2. Reduce rewind tension.

3. Reduce stack height.

4. Use solvents that do not attack prior

coatings.

5. Reduce web temperature by chilling

within ±10° of room temperature or

reducing dryer temperature.

6. Avoid rewinding excess surface

moisture on web prior to rewind.

■ Undesired adhesion

between two

surfaces.

1. Low lamp power setting.

2. Weak exposure bulbs.

3. Dirty lamp reflectors.

4. Lamp focus incorrect.

5. Excessive press speed.

6. Excessive ink film thickness.

7. Lamp shutter not opening.

1. Increase lamp power setting.

2. Replace exposure bulbs.

3. Clean lamp reflectors.

4. Adjust lamp focus to

optimal distance.

5. Reduce press speed.

6. Reduce ink film thickness.

7. Check lamp shutter

assembly operations.

■ Ink fails to cure.

■ Ink offsets in

rewound roll.

■ Ink picks on idle

rollers.

■ Ink tracks through

the press.

DEFECT/INDICATOR PROBABLE CAUSE CORRECTIVE ACTION

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(CONT‘D)

226 FLEXOGRAPHY: PRINCIPLES & PRACTICES

DRYING TOO FAST

DRYING TOO SLOW

FEATHERING

1. Excessive pressure settings.

2. Incorrect solvent balance.

3. Uncontrolled ink viscosity and/or pH

range.

4. Improperly set ink metering applica-

tions.

5. Poor shoulder angles on plate.

6. Dust on the substrate transferring to

the plate.

7. Excessive static electricity present.

8. Dried ink on plates from startup or

previous run.

1. Use minimum pressure settings for

plate and anilox.

2. Use correct solvent balance.

3. Maintain proper ink viscosity and/or

pH range. Use fountain covers.

4. Readjust pressure settings of foun-

tain roll nip or doctor blade assembly.

5. Use a steeper shoulder angle on the

plate with consideration for support.

6. Use web cleaning devices when nec-

essary.

7. Use static eliminator bars.

8. Wash plates thoroughly after color

OK and when order is completed.

■ Irregular string-like

edges around print,

often on trailing

edges.

1. Use of slower drying solvents.

2. Ink viscosity too high.

3. Inadequate or unbalanced drying

equipment.

4. Improper ink formulation.

5. Excessive ink film thickness.

6. Pressroom environment consisting

of low temperature and/or high

humidity.

7. Excessive press speeds.

1. Use faster drying solvents.

2. Reduce ink viscosity. Check viscosity

approximately every 30 minutes.

3. Use adequate and balanced drying

system to accommodate normal

press speeds.

4. Use ink formulation having more

hold-out capability.

5. Reduce ink film thickness.

6. Control pressroom environment to

ideal conditions.

7. Reduce press speeds.

■ Ink fails to properly

dry.

■ Ink pick-off or

transfer to press

rollers and/or sub-

sequent plates.

■ Ink offsetting or

blocking in rewind

or stack.

■ Ink penetration of

paper.

■ Tacky print surface.

1. Improper use of solvents.

2. Low pH level.

3. Uncontrolled or unrestricted air

movement in the vicinity of plates

and rollers.

4. Failure to use fountain covers.

5. Improper ink formulation.

6. Excessive preheat web temperature

entering print stations.

7. Pressroom environment consisting

of high temperature and/or

low humidity.

1. Use proper solvents.

2. Check pH and adjust to optimum

point.

3. Eliminate excessive air movement in

vicinity of plates or rolls by fans,

open windows or doors. Balance air

intake and exhaust flow for between

station dryers.

4. Use fountain covers.

5. Use proper ink formulation for sub-

strate being printed.

6. Reduce preheat web temperature

entering print stations.

7. Control pressroom environment to

ideal conditions.

■ Ink drying on plates

and/or rollers and

failing to transfer.

DEFECT/INDICATOR PROBABLE CAUSE CORRECTIVE ACTION

PRESSROOM TROUBLESHOOTING CHART

(CONT‘D)