ENHANCED PROBLEM SOLVING FOR FLEXOGRAPHIC PRINTING

PROBLEM

POSSIBLE  CAUSE

CORRECTIVE  ACTION

POOR ADHESION

improper ink formula / chemistry

check if the correct ink is used for the substrate being run

ink   thinned   too    much,    binder    in-sufficient

restore and stabilise ink viscosity at optimum level, add fresh ink or resin binder

ink fails tape test

insufficient drying, too low temperatures and/or air volumes in the dryers

increase drying temperatures and or air volume and/or air velocity

Ink requires more
surface slip/release agent

ink fails crinkle test

low surface treatment of the substrate

check surface of the material, apply specific varnish

ink fails scuff test

surface of substrate contaminated

check the stock with the supplier, apply wash coat before printing

substrate requires primer treatment

apply primer prior to printing

BINDING

wrong web tensioning, substrate moves independently of plate movement

adjust web tension, clean and lubricate rollers, check web tension control system

intermittent dark lines of varying density and width, in the printing direction

gear bottoming off pitch line

see ' gear marks'

intermittent plate slur

run bearers

too high ink viscosity

adjust viscosity

non compressive sticky-back

use cushioned sticky-back

low durometer plates

use plates with the proper hardness

BLEEDING

First down color drying too slowly or second down color drying to fast

reduce viscosity and/or ink film thickness of color, use faster or slower solvent, adjust or check drying stations

Second down color wetting into first color
 (overprint, trapping application),  diffused or migrating colors

poor physical  property resistance

use proper ink formulation and pigment grade selection

BLOCKING

improper ink drying

use the suitable solvent mixture

adhesion between two contact surfaces

trapped solvents

adjust drying condition, check solvent balance

(printed and/or unprinted area)

excessive weight in stack

reduce stack weight

BLOCKING

excessive temperature in rewind

reduce dryer heat

adhesion between two contact surfaces

excessive pressure in rewind station

reduce rewind tension

(printed and/or unprinted area)

web rewound  too warm

lower drying tunnel temperature or lower chilling roll temp. within ±10 °C of room temperature

softening of applied coatings

use solvents that do not attract these coating

web rewound with high surface moisture

avoid chilling  that condenses moisture on web before rewinding

BRITTLENESS
  
ink film  substrate breaks or cracks when flexed

excess heat or UV exposure level in drying/curing system causing release of moisture and plasticizer from substrate or ink film

control web or film temperature, reduce heat and /or increase air volume through drying tunnel, reduce UV lamp power

STRONG COLOR

excessive ink viscosity

reduce ink viscosity solvent

excessive color strength or ink transfer to substrate 

unstable mixture of solvents

consult ink supplier to establish the optimum solvent mixture

excessive pigment level

add extender or transparent white

incorrect selection of anilox cylinder

select anilox roll with lower cell volume (bcm) – less volume of ink

incorrect selection of fountain roll for ink transfer

select fountain roll with higher durometer

light setting of fountain roll (if used) nip

regulate fountain roll nip pressure and nip gap

incorrect set-up of doctor blade system

adjust parallel alignment of doctor blades with the minimum required pressure

COLOR VARIATION

lack of viscosity control

maintain viscosity, equip the machine with automatic viscometer

inconsistent color throughout the printing process

lack of pH control (for water  based inks)

maintain pH between 8.0-9.5, use press-side pH meters

inconsistent press run

stabilize and record the process variables, keep records for every press run

variation in ink batches

mix adequately the ink from the warehouse, use ex-proof stirs

color contamination

improve cleanup procedure, filter the used ink

WEAK COLOR

too much solvent or too low ink viscosity

add fresh ink to restore viscosity

thin ink film,
lack of color strength

improper setting of ink roller nip (if used)

lower roller  nip pressure and allow more ink to be transferred to the anilox roll, check mechanical condition of rubber ink roll

improper ink roller for ink transfer (if used)

equip the printing station with the correct rollers (with lower durometer)

WEAK COLOR 

incorrectly specified anilox roll

select anilox with higher ink transfer (higher volumes)

thin ink film,
lack of color strength 

worn anilox roll

replace with new or re-engraved roll

plugged anilox roll cells

clean anilox cells with the proper procedure, advise the manufacturer

ink settling

thoroughly mix ink in container before adding it in the ink vessels

ink pump mis-functioning

check and repair ink pump

excess extender varnish

add pigment concentrate

DOT GAIN

excessive ink volume

use anilox roll with lower ink transfer while maintaining color requirements

excessive plate thickness

use thinner plates, check possible variation in thickness

excessive increase in the size of a halftone dot from film to the printed image

improper sticky-back

use cushioned sticky-back

low ink viscosity

increase ink viscosity

too much pressure between plate cylinder and substrate

reduce pressure

poor ink metering system

use chambered doctor blade system

damaged or worn press components

check and replace defected components, establish preventive maintenance system

dirt on impression and/or plate cylinder

clean impression cylinder and / or plate cylinder

DRYING TOO FAST

improper use of solvents

select proper solvent

low pH lever (for water-based inks)

check pH and adjust to optimum level (8.5-9.5 using pH adjuster/additives)

ink dries on plates and or anilox cylinder

uncontrolled air movement in the area of plates and inking rollers

adjust the dryer to avoid any uncontrolled air movement, eliminate air movement due to open windows, door etc.

excessive preheat web temperature entering print stations

reduce preheat web temperatures (if used)

ink fails to transfer onto substrate

improper ink for the material

select the proper ink for the material being run

dried ink on plates from the set-up of the machine

wash printing plates after the set-up of the machine and before the start of the production in full speed

DRYING TOO SLOW

use of slower drying solvents

use faster drying solvents

ink fails to properly dry

too high ink viscosity

control ink viscosity, use automatic viscosity meters in the press

ink bleed into another (improper trapping)

inadequate or unbalanced drying system

use adequate and balanced drying system and establish stable press runs

ink pick off or transfer to press rollers and/or subsequent plates

improper ink formulation

choose an ink having a more hold out capability

ink offsetting or blocking in rewind or stack

excessive film ink thickness

reduce ink film thickness (see color strong)

ink penetration to paper

pressroom environment consisting of low temperature and / or high humidity

control pressroom environment

tacky surface of the print

Excessive press speeds

decrease press speed

FEATHERING

improper pressure between anilox roll and plate cylinder

Decrease pressure

irregular, string like edges around print area 

ink is drying on the plate or on the anilox cylinder

use proper solvents and covers for the inking station

uncontrolled ink viscosity and / or pH range (for water based inks)

maintain proper viscosity, check periodically pH

improper set ink metering application

adjust properly the pressure of fountain rolls and or doctor blade system

poor shoulder angles on plates

use a steeper shoulder angle on the plate with consideration for support

dust transferred from substrate to plate

clean the substrate when possible, clean plates during the production, reduce tackiness of the ink

dried ink on plates from the start-up or previous runs

wash plates after color approval in the press and when the run is completed

excessive static electricity present

Install  static eliminator bars in the correct position

FILL IN

specks of ink pigments

use well dispersed inks

piling or speckling of excess ink on and around printing surfaces of plates

contamination of ink

filter ink or replace it, check transport and storage conditions

(especially with relation to small type and screen dots)

excessive fine type or screen  for anilox selection

check design or suitability for flexo printing i.e.: sufficient open areas, proper type face etc.

souring or precipitation of ink vehicle

see SOURING

too soft rubber roller (when used)

use harder rollers (increase 10 points Shore A the hardness)

lack of relief height in plate

increase relief height during the plate processing

uncontrolled ink viscosity and / or pH range

establish and maintain the right viscosity and / or pH range, use fountain rovers

incorrect set-up of ink metering system

increase pressure of fountain roll or doctor blade assembly

excessive plate inking

select finer anilox or improve wipe

ink drying to fast, incorrect solvent balance

use slower solvent, increase printing speed

 CURLING

curl towards coated side

excessive moisture, apply heat to edges, use heat guns

Curl over on edges (usually in coated cellophane)

curl away from coated side

low moisture level, apply moisture to edges

FLAT APPEARANCE IN PROCESS PRINTING

improper or worn plates

replace, adjust plate making

hazy, milky printing

too high plate pressure

correct pressure applied to the substrate

low ink viscosity

increase viscosity

contamination of ink

 replace ink

FOAMING

excessive agitation of ink

reduce if possible the flow rate of ink pump, check the operation of the pump

ink foaming in fountain vessel and / or ink vessel

lack of defoamer agents in ink formulation

add defoamer additive to ink

contaminated ink

replace with fresh ink a.s.a.p.
(e.g. iso-propyl alcohol reduces surface tension/breaks foam)

ink viscosity too high

reduce ink viscosity

GEAR MARKS/CHATTER

parallel lines of misprint

gear bottoming of pitch line

adjust overall plate package thickness to pitch line

a hazy, colorless image of the print on inline unprinted areas of film

improperly cleaned metering roll

moisture or solvent trapped in rewind

thoroughly clean anilox roll and / or fountain roll
improve drying with proper drying set-up, reduce tension at the rewind station

HALO

too much pressure between plate and substrate

correct pressure settings

undesired line surrounding a printed image

poor plates or make-ready

check plates, replace if necessary

double edge printing

cupped edges of plate

make new plates and new plates mould, avoid cupping

plate cylinder out of true

inspect plate cylinder roundness and possible wear/damage  of gears, bearings

plate hardness too high

use only recommended rubber plates for printing given substrates

sticky-back too thin and too firm

use compressible sticky-back

HICKEYS

dried ink/particles transferred to the plate

wash plate – filter ink

KICK OUT OF THE INK

incompatible inks or too low/high pH

always use the proper additives

separation, curdling, thixotropic, gelled

improper handling of used ink

check with the ink supplier

MOIRÉ’ EFFECT

anilox screen count to similar to plate screen count, for example a 165 line anilox used with an 85 line screen plate can cause moiré because of harmonic 85 X 2 = 170, to close too 165 line

change anilox, select a screen count appropriate for tone work

undesirable dot pattern in process printing

improper screen angles, angles of screen plates must not be the same with angles of anilox 

use the proper angles, for example 0' magenta (plate), 15' yellow (plate), 30' cyan (plate), 45' anilox cells, 60' black (plate)

MOTTLING

ink too weak or too thin, loss of tack (excessive reduction of viscosity and /or pH level)

add fresh ink and bring it to proper viscosity, adjust pH level,  add varnish to increase tack

uneven surface of plates

remake plates if mottled appearance is evident on surface, examine plate mould for the same mottled pattern

spotted or speckled appearance of solid print

anilox roll cell walls too wide

inspect anilox roll for possible wear, replace anilox

dark or colored intermittent streaks

dirt on plates/impression roller

clean plates, impression roller from inks, waxes and all foreign materials

(usually in a light color)

ink starvation from metering system

adjust the solvent system of the ink (add slower drying solvent)

unevenly absorptive substrates

try softer plates, try more opaque ink

uneven surface of the substrate

try softer plates

contaminated ink

filter ink or replace by fresh ink

ink lacks proper flow

consult ink supplier

PICK-OFF

first color too slow

add fast solvent to first color, increase drying temperature in that station

ink transferring to subsequent plates

second color too fast

add slower solvent, check dryer conditions

second color has too high viscosity

increase press speed and/or reduce viscosity of the second ink

too high pressure of plate cylinder to the substrate

use minimum plate impression pressure

PLATE SWELLING

ink or solvent not compatible with plates

use proper ink and solvents, check quality of plates

residual solvent left in plate from the processing

establish proper processing according to the manufactures of plates

dimensional changes of plate, plate softening

improper handling of plates

proper storing, keep plates protected from UV exposure

PINHOLING

surface roughness of the substrate (irregular or contaminated)

check technical data of the substrate, consult the producer

small holes in solid printed area (not to be confused with hickeys)

failure of the ink system to form a homogenous and continuous film

increase film ink thickness, check dilution rate of the ink, check pressure of anilox and/or plate cylinder, add anti-pinholing compound

dirty central impression cylinder

clean CI cylinder

fast ink drying

adjust solvent mixture, add retarder

POOR INK TRANSFER

ink reduced too much, too low viscosity – metering system determines appropriate viscosity spec

add fresh ink or thick extender

problematic surface of the plates

check plates, clean if they are dirty, replace if they are worn

insufficient ink being applied to the substrate

ink drying on plates and/or in anilox cells

retard system with slower solvent

surface of substrate not receptive to ink system

check surface tension of the substrate, check suitability of the ink, add wetting agent

improper pressure among anilox cylinder, plate cylinder, ink rollers

adjust pressure

low volume transfer of anilox, clogged cells of anilox

use anilox with larger ink transfer capability, clean anilox with the proper solvent mixtures-cleaners, avoid using brushes

SKIPPING PRINT
 (chatter marks)

inconsistent plate calliper

check plate thickness variation (not greater than 0,02 mm), secure new plates or do necessary make ready

areas of plate failing to print

low printing pressures

increase pressure of anilox roll and or plate cylinder

plate cylinder bounce

check concentricity of plate cylinder, gears, impression cylinder. Observe the condition of shafts, journals, bearings and gears for cleanliness or excessive wear

failure to lock down printing deck

be sure that printing stations are locked firmly in place when impression is properly set

print station out of alignment

re-install printing station correctly

SOURING INK
 ink exhibits poor flow and viscosity and has a tendency to curdle

low pH due to evaporation
bacteria growth in old ink

keep fountain rolls covered
maintain pH 8.5-9.5

STREAKS, SMEARS OR SPOTS

gel particles or un-dissolved particles in ink

filter particles out of ink, clean up plates and anilox, advice ink maker

unwanted ink transfer on web surface or liner

ink dripping onto web or sheet

check print stations and ink pumping circuit for overflow or leaks (fountain guards, ink sling rings)

ink throwing off anilox roll

increase ink viscosity, replace end seals or wipers

not proper ink drying

see ' Drying too slow'

excessive foaming

add anti-foam to ink

uneven plates

check plate manufacturing

STREAKS IN WEB DIRECTION

damaged fountain or anilox roll

replace or refinish defective rollers, depending on extent of damage

continuous dark lines through print

nick in doctor blades

hone or replace doctor blades

STRIATIONS

excessive ink transparency

reformulate ink

parallel thin lines or bands present in solid print area

low ink viscosity

replace or add fresh ink

plugged anilox roll cells

clean anilox roll

worn anilox roll

replace anilox roll