Embed Size (px)
Citation preview
FOUNTAIN SOLUTIONFOUNTAIN SOLUTIONFundamentals of Offset DampeningFundamentals of Offset Dampening
Sheetfed OffsetWeb Offset
Sheetfed OffsetWeb Offset Printing auxiliariesPrinting auxiliaries
ReferencesWe would like to thank all companies and institutes for their friendly support with information material and pictures
Figure 1POLYCHROMEOsterode
Figure 3Dr. Herbert BendlinUSF Deutschland GmbHProzess- und Abwasseraufbereitungssysteme
Figure 4Dr. Herbert BendlinUSF Deutschland GmbHProzess- und Abwasseraufbereitungssysteme
Figure 5DRAABE GmbHHamburg
Figure 12Krüss GmbHHamburg
Figure 13Bundesverband Druck e.V."Reduzierung des Alkoholgehaltesim Feuchtmittel"Art. Nr. 86438, 1993
3
Page
From Tap Water to Fountain SolutionWhat kind of water quality is required for offset printing? ......................................................................................................... 4
Methods of Water TreatmentWater softening ....................................................................................................................................................................... 4
Complete demineralization ...................................................................................................................................................... 5
Reverse osmosis ..................................................................................................................................................................... 5
Treatment of deimineralized water ........................................................................................................................................... 5
pH value and ConductivityWhere does the term "pH value" come from?.......................................................................................................................... 6
Importance for offset printing ................................................................................................................................................... 6
Stabilization of pH value .......................................................................................................................................................... 6
Measurement of pH value........................................................................................................................................................ 6
What is "conductivity"? ............................................................................................................................................................ 7
Conductivity and quantity of fountain solution additive ............................................................................................................. 7
Requirements and Tasks in Offset PrintingProtection of printing plate ....................................................................................................................................................... 8
Antimicrobial effect .................................................................................................................................................................. 8
Setting of surface tension ........................................................................................................................................................ 8
Alcohol reduction in offset printing ........................................................................................................................................... 9
Exact determination of alcohol concentration........................................................................................................................... 10
Interactions between alkaline papers and acid fountain solutions ............................................................................................ 10
Increase of pH value in fountain solution ................................................................................................................................. 10
Piling on the blanket ................................................................................................................................................................ 10
Stripping of ink rollers .............................................................................................................................................................. 11
Running blind of printing plates................................................................................................................................................ 11
Corrosion in printing presses ................................................................................................................................................... 11
Modern Fountain Solution Research ........................................................................................................................ 12SunChemical/HARTMANN fountain solution service ............................................................................................................... 12
Problems, Causes, Actions ....................................................................................................................................... 13/14
Table of Contents
4
From Tap Water to Fountain Solution
During the last 30 years offset printingdeveloped into the most importantprinting process. The key for thissuccess is and always has been thehigh productivity and quality as well asthe relatively easy production of theprinting forme.While typographic, gravure printingand screen printing base on physicalprinciples, Senefelder already definedhis printing procedure - lithography(the precursor of offset printing) - as"chemical printing process". Printingand non-printing areas are notseparated by differences in height, butby varying wetting behaviours of theprinting forme towards water and oil.The non-printing areas are hydrophilic,the printing areas are oleophilic.Figure 1 shows the typical structure ofan offset printing plate.Fig. 1: Structure of offset printing plate,
screen dot on non-printing aluminium oxide
Following this principle, the printingprocess does not only require ink, butalso water. This water must showcertain properties, which are reachedby water treatment and specialfountain solution additives, ifnecessary.
What kind of water quality isrequired for offset printing?Depending on its origin, water canfeature very different qualities andcomponents. The assessment of awater quality with "good" or "bad" canpossibly vary very much, because it isinfluenced not only by its components,
but also by the intended use.Therefore...... drinking water should be free of
odour and taste, low in germs andrelatively low in its natrium chloridecontent,
... cooling water should be free ofcorrosive salts
... washing water should be soft withrespect to the needed detergents.
So what are the properties required ofwater used in the preparation offountain solution? Mostly drinkingwater is used, only few companieshave their own fountain. Theregulation for drinking water leaves alarge scope, which means that waterqualities can be very different.Below the typical components, thecomponents relevant for printing aremarked with *:Salts/cations: Natrium, potassium,calcium*, magnesium* and traces ofiron, manganese, zinc and aluminiumSalts/anions: Hydrogencarbonate*,chloride*, sulphate*, nitrate*, phos-phate and silicateGases: Oxygen, nitrogen, carbondioxide and organic combinations andmicroorganisms (drinking water < 100germs/ml).
The influence of these components onthe printing process as well as therecommended limits can be seen infigure 2. If the water quality signi-ficantly differs from these nominalvalues, a water treatment is recom-mended.
Water softeningDuring this process the hardnesscausing components calcium andmagnesium are replaced by indifferentions (natrium) via a cation exchanger.The principle is shown in figure 3. Thesalt content remains unchanged or is
slightly increased. Corrosive anionsand the undesired portion ofhydrogencarbonate in highconcentrations are not removed.Possible variations in the water qualityremain. According to theserestrictions, the softening is only
conditionally suitable for the
preparation of fountain solution. Ionexchangers have to be regeneratedwith a natrium chloride solution after acertain period of operation. Theretained calcium and magnesium is
Fig. 3: Principle of water softening
Ingredients Influence/Problem Rec. Concentr.Hardness formerCalciumMagnesium
Stripping, pH value,running blind of plate
ca. 8°-12° dH
Hydrogen carbonate pH value 100-200 mg/lChloride corrosion 25 ppmNitrate corrosion 20 ppmSulphate corrosion 50 ppm
Fig. 2: Typical components of tap water and theirlimits for offset printing
Tap water (drinking water)
Softened water
Natrium ion
Calcium ion
Magnesium ion
5
again replaced by natrium and theprocess can start again. Residues ofnatrium chloride have to be removed(washed out) before the system canbe used again.
Complete demineralizationThe complete demineralization workson the principle of a ion exchanger.During this process all ions (cationsand anions) are replaced by thecomponents of the water, hydrogenions and hydroxyl ions become water.The result is completely
demineralized water, which e.g. isused in car batteries.Figure 4 shows the principle ofcomplete demineralization. Completelydemineralized water is not suitable foroffset print (see also "Treatment ofdemineralized water").The ion exchangers of the completedemineralization must be regene-
rated with acid and lye. The wastewater has to be neutralized before it isintroduced into the sewage system.
Reverse osmosisThe reverse osmosis is comparablewith a filtration, in this case the "filter"is a membrane. This membrane isonly permeable for the small watermolecules, but not for salts,microorganisms and othercomponents. If water is directed underpressure past a membrane, thestream divides into two part streams:
• an almost saltfree water quality,which comes through the membraneand
• the very salty waste water, which isdirected past the membrane.
Very hard water qualities have to besoftened prior to the osmosis. RO-water also has to be treated for thepreparation of fountain solution (seefigure 5).
Treatment of demineralizedwaterPractical experiences show that waterwithout hardness causing componentsis not very suitable for offset printing.This particularly applies, if norehardening is done by the paper (seealso "interactions of
alkaline papers with acid fountainsolutions"). Hardness causingcomponents have a positive effect onthe ink/water balance. Thereforehardness causing components have tobe added to soft or treated water. Thehardness should be in the range of 8-12°dH (dH - German hardness).In this context two possibilities have tobe discussed:
1. Mixture with tap water:This inexpensive solution can beused whenever the water quality is
constant and no disturbing salts,e.g. corrosive chlorides, areavailable.
2. Rehardening with AQUATREAT:A special additive, which in additionto natural hardness causingcomponents also containspreservatives.
The suitable water quality is one of thepreconditions to guarantee anunproblematic printing process. Inaddition it is absolutely necessary thatthe fountain solution additive has beenadjusted to the application. Nowadaysmodern fountain solution additivescomply with a variety of requirements.• Stabilization of pH value in a
favourable range for printing• Protection against corrosion of
printing plate
Methods of Water Treatment
Complete demineralization
Demineralized Water
cation resin anion resin
natrium ion
calcium ion
magnesium ion
chloride
hydrogen ion
hydroxyl ion
sulphate ion
hydrogencarbonate ion
water molecule
Fig. 4: Principle of complete demineralization
1. filtration 2. softening 3. reverse osmosis 4. conditioning
dischargecalcium and magnesium
dischargesalts and microorganisms
dosagecalcium solution 0.5%
mecanicalfiltration
Fig. 5: Principle of process water treatment using the example of reverse osmosis
6
• Protection against formation ofodour and slime in fountain solutioncircuit
• Specific setting of surface tension toimprove wetting and controlemulsification
• Prevention of insoluble calcium salts(stripping)
• Reduction of piling on blanket• Reduction of IPA proportion• Protection against corrosion
(printing press)
Where does the term "pH value"come from?There are different explanations for thederivation of the term "pH", e.g. lat.potentia hydrogenii or pondushydrogenii. They all have in commonthe reference to hydrogen. The exactscientific definition - negative logarithmof hydrogen ion concentration (activity)is very abstract.
Figure 6 intends to show thecorrelations in a graph: The pH valueis a measure for the acid concen-tration. Pure water, for example, has apH value of 7, which means that acidsand bases are "in balance". For pHvalues smaller than 7 the acidconcentration is increasing and the
bases concentration is decreasing.Correspondingly pH values higherthan 7 mean a higher base concentration and a lower acid concentration.1
Taking into consideration the definitionfor "common logarithm", a pH valuechange of one unit, e.g.pH = 5 to pH = 4 means a tenfoldhigher acid concentration. Conse-quently small changes in pH valuemay have a big influence. Figure 7shows typical pH values.
Importance for offset printingThe acid concentration in the fountainsolution influences a variety ofproperties during the printing process(figure 8): Running clean of printingplate, water takeup/ emulsification ofprinting ink, oxidative drying of printingink, durability of press materials andreaction of fountain solution with papercoating.
Taking all influences intoconsideration, a pH range of 4.8 to 5.3
has established for offset printing inEurope. Inks, fountain solutions andplates have been adjusted to thisrange, a fundamental change of thepH range requires a completely newadjustment of all components.Experiences from other countries, e.g.USA, show that the adjustment toother pH ranges is possible. However,each pH range can only be acompromise between all parameters.
Stabilization of pH valueTo set and stabilize the pH value,fountain solution additives containbuffer systems, which consist ofblendings from acids and bases. Theyonly change the pH value minimally, ifsmall quantities of acid
or alkaline impurities are added andthus guarantee a constant pH value,
even with exterior influences like paperor ink components in the water.
The quality of a buffer system ischaracterized by its buffer capacity(see figure 9). This buffer capacityprovides a measure for the quantity
pH Value and Conductivity
-
0 31 2 4 5 6 7 8 9 10 11 12 13 14
+
base concentration
acid concentration
+
-
Fig. 6: Correlation between acid concentrationand pH value
Solution pH value
gastric liquid 0.9 - 2.3
lemon juice 2.2 - 2.3
vinegar 3.0 - 3.1
fountain solution 4.8 - 5.3
milk 6.4 - 6.7
water, pure 7.0
blood 7.38
sea water 7.8 - 8.2
soap 8.2 - 8.7
limewater 12.3Fig. 7: Typical pH values of various solutions
Fig. 8: The influence of pH value on printing properties
pH value
Running clean (plate)
Water takeup (ink)
Oxidative drying
Corrosion
Attack paper coating
better
lower
slower
higher
stronger
worse
higher
faster
lower
weaker
3 4 65 7
7
of other substances, e.g. calciumcarbonate from paper coating, can beadded, without considerably changingthe pH value.
Buffer systems show characteristicbehaviours (figure 10): The concen-
tration of the buffer (fountain solutionadditive) and the pH value are in no
direct (linear) correlation. That is, thepH value cannot be used to examinethe added quantity of fountain solutionadditive! Such a measure is onlypossible by measuring theconductivity.
Measurement of pH valueThe pH value can be measured withelectronic devices or with test strips.The common test strips show anaccuracy of ca. +/- 0.5 pH units, i.e. a"measured value" of 4.8 can also bereached by a fountain solution with apH value of 4.3. Due to theseinaccuracies the measurement with anelectronic device should be preferred.
These devices show, depending ontheir purchasing price, an accuracy of+/- 0.1 to +/- 0.01 pH units. Acalibration of the used devices shouldbe possible.
What is "conductivity"?Conductivity is a measure for theability to conduct electric current. Insolutions it is caused by breakingdown salts in electrically loadedparticles, so-called ions. The higherthe salt concentration, the higher theconductivity. The conductivity isdetermined by the water quality andthe used fountain solution additive.The conductivity is not relevant for theprintability, i.e. unlike for the pH
value there is no favourable range forprinting, above or below whichprintability problems occur. Despitethis fact we recommend not to exceeda conductivity of ca. 1500 µS forfreshly mixed fountain solutions. Thisrecommendation is based on the
correlation between conductivity andsalt concentration: Higherconductivities (= higher salt concen-trations) may cause corrosion inprinting presses.
Conductivity and quantity offountain solution additiveThe conductivity is a direct (linear)measure for the concentration of thefountain solution additive and withrestrictions can be used to determinethe exactness of the dosage. In thiscontext it has to be considered that tapwater already has a conductivity whichmay influence the measuring result.Only demineralized water has (almost)no conductivity.
The conductivity is strongly influencedby the alcohol concentration (figure11) as well as by impurities from inkand paper components. Therefore adetermination of the concentration isonly possible with freshly mixedfountain solutions and a constantalcohol concentration. On the otherhand a regular measurement of theconductivity allows conclusionsregarding the pollution level of thefountain solution, because: theconductivity increases with increasingpollution.
Detailed measurements of conductivityand pH value as well as the
pH Value and Conductivity
Fig. 9: Stabilization of pH value by good buffercapacity
pH value7.0
6.5
6.0
5.5
5.0
4.5
4.0
bad buffer
good buffer
external influences / time
Fig. 10: Relation between pH value and added quantity
Fig. 11: Conductivity as a function of added quantity
pH value
8
7
6
5
4
30 1.0 2.0 3.0 4.0 6.0 8.0 10.05.0 7.0 9.0
Addition AQUASTABIL K (%)
conductivity (ms)4
3
2
1
0
0 1 2 3 4 5 6 7 8addition AQUASTABIL K (%)
without IPA
with 10% IPA
8
preparation of comparison curves arepossible within the free SunChemical/HARTMANN fountain solu-tion service.
Protection of printing plateThe printing plate mainly has to beprotected in the non-printing areas.Each damage or chemical changeresults in acceptance of ink (toning).The plate protection prevents the so-called machine-down oxide. To acertain extent it is furthermore possibleto protect the water-bearing layeragainst abrasion. In general, it is notpossible to protect the copy layer withthe fountain solution additive.
However, we have to point out thatalcohol replacements may damagethe layer of unbaked positive plates.Baked plates and negative plates aremuch less sensitive.
The water-bearing layer of the printingplate has the following composition(compare figure 12):
Basic material: aluminiumNon-printing layer: aluminium oxide
The aluminium oxide containschannels, which are separated fromthe basic material by a barrier layer.Some channels even reach thealuminium. In this case it is possiblethat the aluminium reacts with salts,water or air, once the printing platestarts to dry (machine stop or machinedown-time).
The product of this reaction, so-called"wild oxide", is very voluminous andable to transfer ink, due to itscomposition and the fact that it clearlystands out. Such points are visible inthe printed image. It is possible towipe out the oxide, but the intervals inwhich the problem will come back, willbecome shorter and shorter.Sun Chemical/HARTMANN fountainsolution additives contain a specialplate protection, which closes thesechannels and/or prevents the airadmission by a sufficient film duringmachine down-times.
Antimicrobial effectDue to their composition, theirtemperature and the constantventilation, fountain solutions are idealnutrient media for bacteriae, yeastsand fungi. This particularly applies toalcohol-free systems. Thesemicroorganisms are not pathogenic,i.e. not noxious but they can causeextensive interferences like odourformation, filling of systems with mudand blocking of nozzles and pipelines.
Our fountain solution additives containsubstances which counteract the germgrowth and thus counteract the abovementioned interferences. Thesebiozides show a twofold effect: on onehand the immediate effect(desinfection) and on the other handthe long-term effect (preservation).The selection of the substances issubject to the rigid regulation forcosmetics.
Setting of surface tensionThe wetting of solid surfaces, e.g.printing plates and rollers, isdetermined by the surface tension of
the wetting liquids, e.g. fountainsolution (figure 13). Liquids with highsurface tensions, e.g. mercury, showvery poor wetting properties, becausetheir drops have a spherical shape.Therefore the liquid films they formtend to break up. Liquids with lowsurface tension, like alcohol, in thecontrary have excellent wettingproperties, because the liquid spreadsacross the surface.
What is the significance of thisbehaviour for offset printing? Fountainsolutions with high surface tensionsform big drops and therefore result inan uneven wetting of the printing plate.To form a closed fountain solution filma significantly higher quantity offountain solution is required than withfountain solutions with low surfacetension. Not all dampeningconstructions are able to transportsuch high fountain solution quantities.If they can transport such quantities,the ink is confronted with a waterexcess, which results in interferenceswith the ink/water balance.
Fountain solutions with low surfacetension do not have these problems,because they form evenly thin, stablefilms. The required reduction of the
Requirements and Tasks in Offset Printing
“wild oxide” screen dot
fountain solutionaluminium oxide
aluminium
Fig. 12: Formation of plate corrosion
mercury water alcohol
Fig. 13: The surface tension of liquidsdetermines their wetting behaviour
9
surface tension in alcohol dampeningunits is reached by using isopropylalcohol (IPA). The effect of IPA can besupported by wetting agents, whichallow a reduction of the alcoholconcentration. With special laboratoryequipment (tensiometer) the exactsurface tension can be determined,which allows a specific setting (seefigure 14).
Alcohol reduction inoffset printingIn addition to the mentioned reductionof the surface tension, alcohol hasother important tasks, like increase ofviscosity to improve the transport aswell as the control of emulsification.
Alcohol evaporates during the printingprocess and therefore cannotconcentrate, while at the same time itcools the printing press. While the
use of wetting agents can alsoguarantee a good wetting, the lowerviscosity (=worse transport) of alcoholreduced systems partly has to be
compensated by an increased watertransport.
The third important task of alcohol isthe control of emulsification. Due tothe nature of the printing process, inktakes up fountain solution and forms awater-in-oil-emulsion. Investigations ofA. Rosenberg (FOGRA) show that thiswater takeup is realized in two steps:
1. First, the so-called bound water,extremely small drops, which arenot even visible under themicroscope, form. The printingplate is not yet running clean.
2. After the ink is saturated with thiswater, larger visible drops ("freewater" or "surface water") form,which cause the printing plate torun clean.
Between the free and the bound watera very sensitive balance exists, whichfrequently can only be reached by theuse of IPA. Alcohol replacements candisturb this balance. The danger exists
that the balance is shifted to thedisadvantage of the free water so thatthe printing plate has trouble to runclean or is not running clean at all.This danger particularly applies forindirect dampening units, where inkand fountain solution come into veryintensive contact at the bridge roller.This behaviour has to be taken intoaccount when formulating alcoholreplacement products.
The alcohol reduction should berealized in three steps:
1. Exact determination of the exactalcohol contents in the laboratoryand possibly reduction to 10-14%.This step can be realizedimmediately, mostly withoutchanging the fountain solutionadditive.
2. Reduction to 5-7%, when using asuitable additive. Before planningany further reductions the printshop should collect experiencewith this setting for an extendedperiod of time.
3. Further reduction to a concentra-tion which still allows a stablequality print.
In this context the followingrecommendations should beconsidered:
• Exact setting of printing press• Good cooling of fountain solution• Increase of water feed, if
necessary• Periodic cleaning of circuit
Requirements and Tasks in Offset Printing
Fig. 14: Tensiometer for the exact determination of the surface tension of fountain solutions
10
• If necessary, use of baked plates• Use of hydrophilic fountain rollers
In addition, the use of treated waterand ceramic rollers have provedsuccessful to some extent.
Exact determination of alcoholconcentrationThe reduction of alcohol only makessense, if the alcohol concentration canbe determined exactly. Regretfully theusual alcohol determination iscombined with uncertainties:Areometer and alcohol doserdetermine the quantity to be added viathe specific gravity of the fountainsolution. The specific gravity of thefountain solution is determined by thealcohol as well as by the fountainsolution additive. Figure 15 shows,how big the influence of the fountainsolution additive can be.
Exact determinations are only possiblevia gas chromatography or specialsensors. Within the SunChemical/HARTMANN fountain
solution service respectivemeasurements are realized.
Interactions between alkalinepapers and acid fountainsolutionsDue to their manifold positive
properties alkaline papers occupy alarge range within the different paperqualities. In contrast to that, fountainsolution additives are still acid.Therefore intensive interactions canbe expected.
Alkaline papers contain calciumcarbonate, which gives papers a goodopacity. Furthermore this veryinexpensive raw material offers goodflow properties of the coatingcompound during the paperproduction. Papers, which containcalcium carbonate do not show thecritical acid decomposition, typical forold documents.
Acid fountain solutions dissolvecalcium carbonate, developing gas,which might cause the enrichment ofcalcium salts in the fountain solution
circuit. This enrichment may cause aseries of printing problems:
Increase of pH value• Piling on blanket• Stripping of ink rollers• Running blind of printing plates• Transparent residues and preci-
pitations
Increase of pH value infountain solutionDue to the reaction of the fountainsolution with calcium carbonate thebuffer substances are used up totallyor partially. Therefore the buffercapacity of the fountain solutionadditive becomes more and moreimportant. An increase of the addedquantity improves the buffer capacity.However, it must not result in adecrease of the pH value, becausethis would intensify the destruction ofthe paper coating and a stabilization ofthe pH value could not be reached(figure 16).
Piling on the blanketBy the reaction of acid with coatingparticles the paper coating starts todissolve, which causes a partial loss ofthe inner coherence of the papercoating. Loose coating particles maypile on the blanket. This error mostlybecomes more evident in the lastprinting units. Special additivescounteract this problem, by facilitatingthe removal of the coatingcomponents.
Requirements and Tasks in Offset Printing
Specific Gravity Concentration Real Alcohol Concentration (%)Additive (g/ml) Additive (%) 4 6 8 10 12 14 16 18 20 22
1.052 3.1 5.1 6.8 8.7 10.5 12.4 14.2 16.1 17.9 19.73 2.8 4.6 6.4 8.2 10.1 11.9 13.7 15.5 17.3 19.14 2.5 4.3 6.0 7.8 9.6 11.4 13.1 14.9 16.7 18.5
1.102 2.5 4.3 6.1 7.9 9.7 11.4 13.2 15.0 16.8 18.63 1.9 3.6 5.3 7.0 8.8 10.5 12.2 13.9 15.6 17.44 1.2 2.9 4.5 6.2 7.9 9.5 11.2 12.8 14.5 16.1
1.152 1.9 3.6 5.3 7.1 8.8 10.5 12.2 14.0 15.7 17.43 0.9 2.6 4.2 5.8 7.5 9.1 10.7 12.3 14.0 15.64 0.0 1.5 3.0 4.6 6.1 7.6 9.2 10.7 12.3 13.8
1.202 1.3 2.9 4.6 6.3 7.9 9.6 11.2 12.9 14.6 16.23 0.0 1.5 3.1 4.6 6.1 7.7 9.2 10.8 12.3 13.84 -1.3 0.1 1.6 3.0 4.4 5.8 7.2 8.6 10.0 11.4
Fig. 15: Influence of fountain solution additive on alcohol dosage. The values of the tableare measured by areometer
3 4 5 6pH value
abra
sion
Fig. 16: Influence of pH value on abrasion ofpaper coating
11
Stripping of ink rollersThe calcium ions dissolved in thefountain solution react with the citratesfrequently contained in the buffers andform insoluble salts.
Fig. 17: Ink rollers with residues
These are stored in the pores of theink rollers, which consequentlybecome hydrophilic. The waterinfiltrates the ink film, the ink isdisplaced and the ink rollers partly dono longer transport ink (= stripping).The regeneration of stripped ink rollerscan only be realized with specialwashing agents (ROLLERFIT), whichare able to dissolve the insolublecalcium salts (see figure 17).
Running blind of printing platesIn addition to the mechanic wear therunning blind of printing plates canalso be caused by insoluble calciumsalts. These hydrophilic salts depositon the printing plate. The ink film onthe copy layer is infiltrated by water,the ink is expelled and the ink is nolonger transferred to the printing areas(running blind of printing plate).Special fountain solution additives withthe following properties counteractthese problems:• low attack on paper coating
• prevention of insoluble calciumsalts (see figure 18)
• good buffer capacity• minimize piling on blanket
Corrosion in printing presses
The corrosion behaviour in printingpresses is decisive for the selection ofthe materials. Materials like steel,alloyed steel and nickel steel can beconsidered. Inhibited fountain solutionadditives can considerably reduce thecorrosion of these materials. Byelectrochemical measurements andimmersion trials, in which the loss ofweight of a substance sample isdetermined, the corrosion behaviour isinvestigated in the laboratory. Figures19a and 19b compare the theoreticaland practical behaviour of inhibitedand non-inhibited systems.Non-inhibited systems show aconstantly progressing mass loss.
Inhibited systems, however, only showa light corrosion at the beginning,which rapidly reduces considerably.The use of corrosion inhibitorsremains however without effect, if youdo not consider other influences as
well:
• Machine maintenance• Water quality (we especially refer
to the limits of 25 ppm for chlorideas well as 50 ppm for sulphate and20 ppm for nitrate recommendedby the German printing association(Bundesverband Druck))
• Ink, paper and other consumermaterials
The whole concept must be orientedon the protection against corrosion.
Requirements and Tasks in Offset Printingpr
ecip
itatio
n qu
antit
y
additive 1 additive 2 additive 3
Fig. 18: Influence of fountain solutioncomposition on formation of calcium salts
abra
sion
rate
non-inhibited
inhibited
+
-time
Fig. 19a: Determination of nickel mass loss. Theoretic behaviour of inhibited andnon-inhibited systems
Fig. 19b: Determination of nickel mass loss. Practical behaviour of inhibited andnon-inhibited systems
abrasion rate (mg/cm²)20
15
10
5
01 2 3 4 5 6 7 8 9 10 11 12 13 14
time
non inhibited
inhibited
12
Modern fountain solution additives arehigh tech products. In order to copewith the permanently changing andincreasing requirements, wellequipped laboratories are required. AtSunChemical/HARTMANN we havethe possibility to determine watertakeup and ink/water balance with theLithoLab-Tester (figure 20) and tooptimize them specifically.
These investigations are supported bymeasurements with the Lithotronic
measuring instrument (figure 21),which examines the rheology (flow andtransfer characteristics) of theemulsion.The specific setting of the wettingbehaviour is realized by measure-ments with different tensiometers (seefigure 14). The development ofcorrosion inhibited fountain solutionadditives is realized with anelectrochemic setup. This extensiveequipment allows a considerablybetter insight into the offset printingprocess.
Sun Chemical/HARTMANNfountain solution serviceNo water quality is identical withanother one, because print jobstructure and general conditions canvary considerably. Furthermore therequirements regarding quality andproductivity are constantly increasing.Therefore service and support by thesuppliers are of decisive importancefor print shops:
• Water analysis to evaluate thesuitability for printing and thecorrosiveness of the water
• Examination of dosage for additiveand IPA as well as setting ofreference curves (figure 22)
• Consultation for planning of watertreatment systems and optimi-zation of fountain solution supply
• Creation of a report concerning thebacterical status in large systems
• Comprehensive documentation,technical information and materialsafety data sheets.
Modern Fountain Solution Research
Fig. 20: LithoLab tester for investigationof ink/water balance
Fig. 22: Documentation SunChemical/HARTMANN fountain solution service
Fig. 21: Lithotronic to optimize ink/water emulsion
Fountain Solution Analysis
Customer: Smith ExpressStreet: Anfield Road 10Town Country: Liverpool UKContact Person: John Smith
Date: 31.10.1997Report No.: 971142
Sample: Fountain solution
pH-Value: 5,5
Conductivity: 1575 µS
IPA-Content (GC): 2 vol.%
Ethanol-Content (GC): 12 vol.%
Assessment of Fountain Solution:The characteristic values of the fountain solution are in the range of tolerance. Theconductivity indicates that the concentration of the dampening additive is round about3 percent (see graph).
Fountain Solution Analysis
Customer: Smith ExpressStreet: Anfield Road 10Town Country: Liverpool UKContact Person: John Smith
Date: 31.10.1997Report No.: 971142
Sample: Fountain solution
pH-Value: 5,5
Conductivity: 1575 µS
IPA-Content (GC): 2 vol.%
Ethanol-Content (GC): 12 vol.%
Assessment of Fountain Solution:
The characteristic values of the fountain solution are in the range of tolerance. Theconductivity indicates that the concentration of the dampening additive is round about3 percent (see graph).
Water Analysis
Customer: Smith ExpressStreet: Anfield Road 10Town Country: Liverpool UKContact Person: John Smith
Date: 31.10.1997Report No.: 971142
Sample Tap Water
pH-Value: 7,5
Total Hardness: 1,73 mmol/l (9,6 ° d.H.)
Hydrogencarbonate: 186 mg/l
Conductivity: 442 µS
The water is with 9,6 ° d.H. medium hard and suited for the offset printing.
Recommendation:
For this water quality we recommend the use of 3 % AQUASTABIL KH 5471 with 10 vol.% of the isopropylalcohol/ethylalcohol-mixture. The fountainsolution should have a pH-value of 5,3 and a conductivity of1300 µS (see graph).
We can't recommend the unusual application of an ethylalcohol/isopropyl-alcohol-mixture which affects strongly the airquality. Due to the higher evaporation rate ofethanol in comparison with isopropanol a higher ethanol concentration in the fountainsolution is necessary and the alcohol concentration in the air is higher.
Water Analysis
Customer: Smith ExpressStreet: Anfield Road 10Town Country: Liverpool UKContact Person: John Smith
Date: 31.10.1997Report No.: 971142
Sample Tap Water
pH-Value: 7,5
Total Hardness: 1,73 mmol/l (9,6 ° d.H.)
Hydrogencarbonate: 186 mg/l
Conductivity: 442 µS
The water is with 9,6 ° d.H. medium hard and suited for the offset printing.
Recommendation:
For this water quality we recommend the use of 3 % AQUASTABIL KH 5471 with 10 vol.% of the isopropylalcohol/ethylalcohol-mixture. The fountainsolution should have a pH-value of 5,3 and a conductivity of1300 µS (see graph).
We can't recommend the unusual application of an ethylalcohol/isopropyl-alcohol-mixture which affects strongly the airquality. Due to the higher evaporation rate ofethanol in comparison with isopropanol a higher ethanol concentration in the fountainsolution is necessary and the alcohol concentration in the air is higher.
AQUASTABIL K H 3949 in Tap Water of Smith Express with 10 vol.% of isopropylalcohol at 23 °C
200
400
600
800
1000
1200
1400
1600
1800
2000
0,5 1 1,5 2 2,5 3 3,5 4 4,5
Concentration AQUASTABIL K H 3949 [%]
Con
duct
ivity
[µS]
AQUASTABIL K H 3949 in Tap Water of Smith Express with 10 vol.% of isopropylalcohol at 23 °C
200
400
600
800
1000
1200
1400
1600
1800
2000
0,5 1 1,5 2 2,5 3 3,5 4 4,5
Concentration AQUASTABIL K H 3949 [%]
Con
duct
ivity
[µS]
13
Problem Definition Possible causes ActionspH value pH value outside the
range4.8-5.5 (heatset),5.0-5.5 (sheetfed)
not enough fountain solutionadditive, wrong buffer setting;use of alkaline papers
verify/correct dosage; select product with acidsetting; product with higher buffercapacity/lower attack on paper coating
Stripping disturbed ink acceptanceon ink rollers, no inktransfer
insoluble calcium salts fromwater, ink, paper (main source)
clean rollers with ROLLERFIT, use of fountainsolution additive which counteractsstripping/insoluble calcium salts, set pH valueat upper tolerance limit to pH 5.1-5.5
Residues/precipitations
white residues/cristals incircuit or on plate andblanket
see "stripping" see "stripping"
Running blind/plate disturbed ink transferfrom plate; disturbed inkacceptance of copy layer
see "stripping" see "stripping", do not clean plate withROLLERFIT, damage of plate possible
Plate wear copy layer
non-printing area
wrong press setting; use ofaggressive fountain solutions
wrong press setting; insufficientplate protection
check press setting 0.15 mm pressureplate/blanket; possibly plate or developmenterror; positive plates are partly attacked byalcohol replacements: burn in plate, ifnecessary, change plate type or fountainsolution
see above; use of fountain solution additivewith better plate protection
Plate corrosion "Bubble formation" onplate and print
insufficient plate protection; alsoinfluenced by plate quality
use of fountain solution additive with betterplate protection, if necessary, change platetype
Poor drying prints do not dry or drytoo slowly
ink unsuitable for substrate; pHvalue of fountain solution toolow; influence of substrate; watertakeup of ink too high
change ink type, e.g. do not use fresh ink onfoils or low-absorbency substrates; set pHvalue at upper tolerance limit to pH 5.1-5.5;use special additive on foils, adjust ink tosubstrate, if necessary, change substrate.See also "emulsification"
Foaming fountain solution foamson return
washing agent or similar incircuit, return output too high;strongly foaming fountainsolution additive
mix new fountain solution, avoid washingagent in system, if necessary use defoamer,reduce return/pumping capacity, return belowwater surface, if necessary, change additive
Piling/blanket within printed image:positive piling
outside printed image:negative piling
ink tack/picking resistance ofpaper not adjusted to eachother; attack on paper coating byacid fountain solution
ink/water balance, washing outof ink
if possible, reduce ink tack, if necessary,change paper quality; fountain solutionadditives with additive against piling; set pHvalue of fountain solution at upper limit to pH5.1-5.5
coordinate fountain solution and ink, error isalso influenced by paper quality (absorbency,coating components)
Problems,Causes, Actions
14
Problem Definition Possible causes ActionsRunning clean/plate at start or after press stop
printing plate does not oronly slowly run clean
pH value too high; alcoholconcentration too low; plateprotection not sufficient; presssetting not correct, ink/waterbalance disturbed
set pH value at lower tolerance range topH 4.8-5.1, monitor ink drying and reaction withpaper coating; examine alcohol concentrationand correct if necessary; examine and increaseadded quantity of fountain solution additive ifnecessary; examine settings, possibly pressureof dampening rollers too low; adjust fountainsolution/ink to each other
Toning non-printing area transfersink, partly only slightcoloration. See also platecorrosion
pH value too high; plateprotection not sufficient; plateinsufficiently developed; inktransfer too high (rathersmearing); residues on plate orblanket; alcohol concentration toolow; ink/water balance;insufficient temperature control
set and examine pH value; examine andincrease added quantity, if necessary; checkplate development; reduce ink transfer;eliminate cause for residues; check alcoholconcentration; check water takeup of ink,adjust fountain solution/ink; check temperaturecontrol of ink or dampening unit
Smearing non-printing areas transferink
insufficient water transport, see"Toning"
check press setting, check alcoholconcentration. See "Toning"
Flying ink/water emulsion istransported to the rolleredges and is flying
water takeup of ink is too high;press setting
check alcohol concentration, if necessary,adjust ink/fountain solution. See also "Misting"
Misting occurs across the wholewidth of the roller, mostlypure (not emulsified) ink
rheology of ink; roller setting toostrong; insufficient temperaturecontrol of inking unit
discuss rheology change of ink with inkmanufacturer; check roller setting, checktemperature control of form roller; checktemperature control of inking unit
Emulsification printing ink takes upwater, emulsification isdesired. Emulsification oftoo much water = instableemulsification
wrong roller setting; pH value toohigh; dosage of fountain solutiontoo high; dosage of IPA too high;water too soft; too little inkconsumption
check roller setting; check and set pH value(nominal: 4.8-5.3); check and set dosage offountain solution additive; check and set IPAdosage; set hardness to 8-10°dH; also print inkconsumption strip.
Instableemulsification
see "Emulsification" see "Emulsification"
Microorganisms formation of odour andslime in circuit
dosage of fountain solutionadditive too low; tap water(fountain or ion exchanger)contains too many germs;formation of resistant germs
before taking any measures, diligently cleanthe system (cleaning concentrate), checkdosage of fountain solution additive, checkwater quality, change preservation agent ifnecessary
Dot gain water takeup of ink too high;see "Emulsification"; adjustmentink/substrate
see "Emulsification"; adjust ink to substrate
Problems,Causes, Actions
