Fountain Water in Offset Printing

Task

The operating principle of offset printing is based onthe natural reaction that grease and water will repeleach other. Whereas the printing areas accept the

“greasy” printing ink, thedamping water will berepelled. The non-printingareas are hydrophilic andwill repel the printing ink.

First the printing platewill be wetted by the

damping unitwith a thindampingwater film,

then the printingareas are inked up with

printing ink by means of theplate inking rollers. The printed

image is then transferred to ablanket cylinder and transferred from

there to the printing material. This is whyoffset printing is also called an indirect printingmethod.

Fountain additives are concentrated additives takingover a series of functions and tasks. Apart fromvarious protecting functions, the fountain additive willinfluence the physical-chemical properties of thefountain water, will facilitate and optimize the printingprocess.

In the following the most important components andtasks of a fountain additive are listed. The compositionand development of these additives is based on amaximum of competence and know-how. In mostcases more than 25 raw materials and their combinedeffects are responsible for an optimum functioning ofa fountain additive such as Schwego® Soft.

Components

Buffer SystemThe buffer system sets a pH-value of 4,8 - 5,2favourable for printing. In spite of various influencingfacts such as quality of water, contamination by ink,washing agents or similar factors the pH-value is“buffered” – i.e. a constant value is maintained asrequested.

Tenside-/Emulsifying Agent SystemIt will control thechemical and physicalreaction of theinteraction betweenprinting ink, fountainadditive and printingplate. Among themare, for instance, thewater-absorbingcapacity of the printingink (amount andspeed) and the optimum limit and surface stress.

Complexing AgentsReactions between the materials will be caused byvarious deposits from printing ink, paper and fountainwater, and might considerably disturb the productionprocess.

Fountain Waterin Offset Printing

Important Characteristic Features of theOffset Printing Method:

Sheet-fed offsetThe printing material is printed sheet by sheet.Apart from some speciality printing processes themain production method is job printing. Theprinting inks will dry by absorption/oxidatively.

Web offset:The printing material is printed continuously fromthe “reel”. There are three possibilities –newspaper printing (coldset), commercial printing(heatset) and continuous stationery printing.Whereas in newspaper printing the ink will dry byabsorption, in heatset printing the ink is driedphysically by a hot-air dryer. The continuousstationery printing process is similar to sheet-fedoffset printing considering the process with justone difference: the printing material is printed“continuously”.

Water drops above:high surface tensionWater drops below:low surface tension

Inking unit

Plate cylinder

Blanket cylinder Continuous-feeddamping system

Impression cylinder

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An essential factor in this context is the calcium andmagnesium hydrogen carbonate. There is a possibilitythat it will accumulate and disturb the ink transportby its hydrophilic characteristic. Chosen complexingagents will bind these salts and reduce the deposits.

PreservativesThe fountain water will contain a large number offoreign substances especially by the printing process,and these substances will contain the nutrientspreferred by germs, such as paper dust. In addition,the formation and increase of bacteria, yeast and moldfungi is assisted by the development of heat, longfountain water circulations and idle operatingconditions in the fountain water circulation.In order to prevent the formation of germs, con-servation agents are added to the fountain solution.The biggest risk of germ formation is in newspaperprinting. In job printing in most cases alcohol (IPA) isadded to the fountain additive. Apart from the reliefoffered from the point of view of printing technology,alcohol will also impede the formation of germs.

Protection of Printing PlateIn order to protect the surface of the printing plateagainst oxidation and foreign matters during anyinterruptions of the production process, chosencomponents will form a protective layer on theprinting plate during a dead halt of the machine.

DrierIn contrast to web offset, penetrating/oxidativelydrying inks are used in sheet-fed offset printing.In order to speed up the oxidative drying process,it is possible to add a drying agent, such as Schwego® Drier 8141, to the fountain solution.As an alternative we offer Schwego® Soft 8128/8129and 8157, fountain additives with integrated dryingagent with different pH-value settings. All the dryingagents processed by us are free from cobalt which isdetrimental to health and ecologically harmful.

InhibitorsIn order to protect machine parts from corrosion,inhibitors are added to the fountain additive.Schwego® Soft is always equipped with inhibitors, thefunction of which is tested and released by leadingmachine and plant engineering companies.

SolutizerIn order to stabilize all listed components in asolution over a prolonged period of time, suitablesolutizers are used. These solvents often have got adecisive influence on the ecological compatibility ofthe fountain additive.

EnvironmentDue to the complex composition of a fountainadditive the topic “environment” will play acomprehensive part in the development of theproducts as well. Especially VOC-contents, type ofmeans of preservation, possibilities of wastedisposal and product identification are catchwordspermanently used. There is an EC-specification sheetfor security which contains all safety references.As Schwegmann company is an extremely en-vironmentally aware company, we will always be apioneer in the development of environmentallycompatible products.

Parameter of the Fountain Waters

Water QualityThe basis of the fountain water is the industrial waterused. From the point of view of printing technologyspecial focus should be on the salt contents of thewater as cause of its degree of hardness resultingfrom the two water hardness factors total hardness(TH) and carbonate hardness (CH).

A constant water quality with a total hardness of 8-12° dH (illustration: all salts contained in the “hardness forming salts” area) is recommended. Ourresearch and experience show that the emulsifyingstability of printing ink and fountain water is positivelyinfluenced as from a total hardness of 8° dH.

The carbonate hardness consisting of the hydrocarbonates (HCO3) has got a decisive influence.(Illustration: all salts listed in the lowest line.)On the one hand the naturally “alkaline” hydrocarbonates will react with the “acid” component ofthe buffer system in the fountain water, which willlead to an increase of the pH-value. On the otherhand calcium and magnesium bicarbonate (illustration:red area) will lead to undesired lime deposits. Thesedeposits will be especially interfering on inking rollersand damping rollers. As described above, they willinterfere with the emulsifying behaviour and the inktransport by their hydrophilic or ink-repellentcharacteristic.

In order to optimize the water hardness degrees forthe printing process and to avoid any possiblevariations in the water quality of the local watersupplier, quite often waste water treatment plants areused for standardizing the fountain water. For thispurpose plants for softening or desalting the waterare a possible solution.

Softening EquipmentWhen softening the water, calcium and magnesium(illustration: transparent oval) are replaced by sodiumin an ion exchanger.The remaining hydrocarbonate(HCO3) will then combine with sodium to form freelysoluble, not hardness forming sodium bicarbonate(NaHCO3).After this process only “non hardness forming” saltsor carbonates are left which will have the mentioned“alkaline” influence on the pH-value.Please note: After the softening it is only possible todetermine the carbonate contents in form of sodiumbicarbonate and potassium bicarbonate, however, notthe carbonate hardness or total hardness. As nohardness formers are left, conventional carbonatehardness tester will supply distorted results.

Salts in naturalwater

Fountain Waterin Offset Printing

not hardness forming salts

hardness forming salts

permanent hardness formers

temporary hardness formers (CH – will form lime deposits)

Transparent ovals, shares of calcium and magnesium TH

NaClsodium chloride

KClpotassiumchloride

Na2SO4sodium sulphate

K2SO4potassiumsulphate

NaHCO3sodium

bicarbonate

KHCO3potassium

bicarbonate

CaCl2calcium chloride

MgCl2magnesium chloride

CaSO4calcium sulphate

MgSO4magnesium sulphate

Ca(HCO3)2calcium hydrogen carbonate

Mg(HCO3)2magnesium hydrogencarbonate

Salts in naturalwater

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In order to reach again the total hardness re-commended for printing, as a rule the softenedwater is diluted in defined quantities with waterfrom the main.

Desalting Plants:In most cases a reverse osmosis plant is used fordesalting. In this case all salts in the water areremoved. In order to reach the total hardness ofabout 10° dH which is recommended for theprinting process, a hardness increasing agent such asSchwego® dH-Fix 8230 is added to the desaltedwater. These hardness increasing agents will form thedesired total hardness only by means of “permanent”hardness salts.

pH-valueThe pH-value indicates the strength of an acid (0) oralkaline solution (14) on a logarithmic scale of 0-14,with the neutral range being around pH 7. The specialthing about the pH-value scale is that a 10-fold changewill take place from one to the next pH-value. Thismeans that a pH-value of 4 is 10-fold more acid thanpH 5 and 100-fold as acid as pH 6.

The pH-value of water from the main or of treatedwater is in most cased in the range between pH 6.5and pH 9. In order to reach the optimum pH value forthe printing process which is between 4.8 and 5.2 theabove mentioned buffer systems are integrated in thefountain additive. Depending on the existing carbonatehardness the buffer capacity is adjusted to the desiredpH-value and kept at a constant level.

Electric ConductanceThe electric conductance indicates the material-specific electrical conductivity for the electricalcurrent in µS (Micro Siemens).

A fountain additive contains large quantities ofchemical compounds which are good conductorswhen dissolved in water. This makes possible todetermine the actual concentration of the fountainadditive in a new compound formulation by meansof the electric conductance.

When measuring in the fountain water circulation,you have to take into account that the measured valueis distorted by foreign matters such as paper, ink andwashing agent components.

The electric conductance will not give any informationas to the quality with reference to the behaviour inprinting technology. In this case the type of the usedsalt is important.

TemperatureThe fountain water temperature should preferablybe about 10-12°C. The constant temperatureequalization will help to stabilize the productionprocess by cooling the machine and ambienttemperature.

pH-value-diagram

Dose Effect Curve

acid

alkaline

pH-value

Hyd

roge

n io

nic

stre

nght

(m

ol/L

)Concentration of fountain additive (%)

pH-v

alue

Con

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(µS

/cm

)

Printing process

Apart from the up to now description of the functionand task of the fountain water, the industrial offsetprinting process also holds a series of difficultiesconcerning the technological process.

The special challenge in offset printing is the emulsionbehaviour of printing ink and fountain water. Theprinting process requires that both materials willemulsify in a certain ratio and at a defined speed andwill remain stable during production printing. Theemulsion behaviour on the other hand is interactingwith a number of variable parameters which make theprinting process difficult to control and reproduce.

Apart from the printing ink and the fountain additive,mainly mechanical influences, materials used, theirconditions of use and their state will play a decisivepart. Among them are inking rollers and dampingrollers, type of damping system, blanket, quality ofwater, temperature, printing substrate, type ofmachine and many more factors.

In addition process-caused alterations such as ink andpaper coating build-up on the blanket or dampingrollers, temperature changes in the printing press,intermediate washing at the blankets and/or dampingsystem, wear and tear of the printing plate and manymore factors will make impossible any productionprinting in a constant quality across long productionruns.

The biggest influence has got the press operator inthis case, who apart from his technical competencewill sense by his experience and feeling for theprinting process which “keys and screws” he will haveto turn in order to get an optimum of quality andperformance from the printing press. Unfortunatelythese personal characteristics are pushed into thebackground to an increasing degree because of theincreasing degree of automation.

Alcohol reduction and eliminationIn the field of job printing in offset printing (sheet-fedoffset and heatset printing) in most cases isopropylalcohol (IPA) is added to the fountain water. Thealcohol will take over several functions and willfacilitate the printing process.Since the invention of the alcohol damping system it istried to substitute the alcohol because of environ-mental and cost reasons. Whereas formerly theproduction was made with partly more than 20 % ofIPA, nowadays a decreasing to 8 % is relatively un-problematic.

This was mainly realized by the latest technology inmetering and proportioning technology for IPA infountain water. In addition, the supplies for theprinting industry adjusted their products to therequirements of the IPA-free printing process. We,too, offer special Schwego® Soft variations for thispurpose.If a considerable reduction or even an elimination ofIPA in fountain water is to be carried out, an increaseddegree of care and sensitivity is needed. The successof alcohol reduction depends on the optimization ofthe whole printing process.

The mentioned functions of the IPAs will mainlybring about an increased production safety andstability, or expressed in another way, with IPAsmaller deficiencies and a little carelessness withinthe production process can be concealed.

In the following some tips for use are given, whichshould be especially observed in case of IPA reductionand elimination, however, very often are neglected.

Effect of Isopropyl Alcohol (IPA):

� Quick, stable ink-water balance

� Lowers the surface tension

� Cools by latent heat

� Avoids germ formation

� Self-cleaning effect

� Increases the fountain water viscosity

� Impedes the formation of foam

� Decreases ink build-up on the dampingrollers

� Damping of comb stripes (surfacewaves)

Fountain Waterin Offset Printing

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Tips for Use

Adjustment of the Inking and Damping RollersToo strong roller stripes (contact of the individualrollers with each other) will have a negativeinfluence on the emulsion behaviour caused bythe mechanical stress and development of heat. It isrecommended to observe the instructions of themachine builder, whereas up to 20% lower values canbe used in case of heated rollers. Transparent andflexible control stripes for the correct roller adjust-ment can be obtained by Schwego® Soft users free ofcharge.

Regular Roller TreatmentThe cleaning and maintenance of the inking anddamping rollers with special cleaning agents is veryeffective. Soil particles, especially deposits of limefrom fountain water, paper and printing ink, will leadto a hardening and surface smoothing of the inkingand damping rollers. As a consequence the emulsionforming is disturbed, which, in turn, will lead to aninstable production printing behaviour with littlescope in the ink/water balance. A cleaning agent suchas Schwego® Clean 8179 will remove the dirt and thelime deposits from the pores of the roller. The surfaceof the roller will get supple again and open-pored.Printing ink and fountain water will be taken up andtransported again much better which will lead to aclearly more stable ink/water emulsion.

Reduced Flow of Ink/WaterEspecially after the above described roller treatmentit will become clear which potential is available con-cerning the production process stability. Quite oftenthe ink and water values can be drastically reduced (-50 %) without any decreasing of the ink density. Onthe contrary the ink/water emulsion will not be that“greasy” any more, the tendency to scumming is less,

the screen dot will print sharper, the ink build-up atthe metering rollers and the blanket will be con-siderably reduced. Please note:“As little ink andwater as possible!”

The best conditions for the production process aregiven, if the printing is done near to the “smearinglimit” – the moment in which there is just enoughwater in order to keep the non-printing areas freefrom ink. In most cases the “smearing” will start at theouter edges of the printing substrate in printingdirection. The causes are often not completely closedink zones in the non-image areas or run in ductrollers which let too much ink into the roller frame atthe edges.Tip: Reduce the duct roller stroke, increase the inkkey opening in the printing area!

In addition, it is recommended depending on thesubject, to use the diagonal adjustment of themetering rollers for continuous-feeddamping systems.

Temperature conditionsSpecial attention should be paid to thetemperatures, especially on high-volumeand fast running machines.In general the heat development at theprinting press is to be well conductedaway. In contrast to this recommenda-tion you will often see protectinggratings for rollers which are maskedbecause of spraying and fogging ink inorder to keep the machine clean. As aconsequence, however, the whole rollerframe will heat up which will causedisturbances of the emulsion behaviourin this case as well.

As far as a temperature equalization ofthe oscillating ink rollers is existing, itshould be at about 26° C at the returnmovement.

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4 mm

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8 mm

9 mm

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12 mm

Transparent, flexible control stripe for theroller adjustment

Bernd Schwegmann GmbH & Co. KG · Wernher-von-Braun-Straße 14 · 53501 Grafschaft-Gelsdorf · GermanyTel.: +49 (0) 22 25 / 92 26-0 · Fax: +49 (0) 22 25 / 92 26-33 · E-mail: info@SchwegmannNet.de · www.SchwegmannNet.de

The fountain water temperature at the returnmovement should possibly not be more than about12° C, whereas the lower temperature limit in weboffset is limited in most cases by the formation ofcondensation water. Water drops falling down on thepaper web might lead to annoying web breaks andconsequently to production interruptions.

Fountain Water MaintenanceOily or greasy components in the fountain water haveto be avoided.As described in the beginning, offset printing is basedon the principle that ink (grease) and water arerepelling each other. If oily cleaning agents which canbe mixed with ink and fountain water get into thefountain water when the blankets are cleaned, thefunction of the fountain water will be reduced ofcourse. If, however, ink and grease components floaton the fountain water, it is recommended to useSchwego® Sorb 8225. This special fibre pad will floaton the surface and bind the oily and greasy coatings.

If damping rollers are cleaned with oily cleaners, anink-receptive film might form on the damping rollersin some cases. By this the renewed soiling by printingink is supported and the formation of a water film isinterfered with.

In case of a manual cleaning of the fountain rollers inthe continuous-feed damping system a thicker layer ofink should be carefully squeezed with a spattle. Afterthat it is possible to remove the ink with a quicklyvolatile cleaner such as Schwego® Damp 8174. Afterthat it is recommended to rub the damping rollerwith a hydrophilic substance such as gum Arabic orprinting plate gum.

In case of a considerable soiling of the fountainwater especially by nucleation, the fountain watercirculation will have to be rinsed or cleaned with aspecial cleaner such as Schwego® Fix 8110.

Use biocides safely. Always read the label and productinformation before use.

© Bernd Schwegmann GmbH & Co. KG Any reprinting or reproduction of the contents evenin extracts is only permitted with written consent ofBernd Schwegmann GmbH Co. KG

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