Fountain Solution
in Offset Printing
INK ACADEMY
Fountain Solution in Offset Printing
Interaction between ink and water_______________________________________ 2
The basis – water______________________________________________________ 3
Demands on fountain solution concentrates______________________________ 4
Monitoring parameters in the fountain solution____________________________ 5
Alcohol in the fountain solution__________________________________________ 7
Corrosion protection in offset presses____________________________________ 7
Microorganisms in the fountain solution__________________________________ 8
Metering fountain solution concentrates__________________________________ 8
Fountain solution waste from print shops_________________________________ 8
Grain: The fineness of the pores and
roughness of the surface of a printing plate
Emulsion: A mixture of two,
technically speaking, non-miscible
liquids that are finely distributed
and show no signs of separating
Non-image areas
Interfacial surface tension:
Forces that arise between surfaces
of substances that are present in
different forms – solid, liquid, gaseous
HH
O HH
O
HH H
H
O
O
OH
OH
OH
OH
Image areas
Attracting the water
Ink
R
Ink
R
R
R
R
R
Attracting the oily ink
Fig. 1: Diagram of the wetting
phenomena
–R = organic molecule
group
–OH= hydrophilic
substance groups
H
H O = H2O = water
2
R
R
Interaction between ink and water
The offset process is the only printing process in which two different liquids are used
on the printing forme. One of these liquids, the viscous ink, is – and is supposed to be
– visible after completion of the press run, while the other one, the fountain solution, is
only visible in the print image if something has gone wrong. When viewed this way, the
fountain solution seems to assume a high degree of importance only whenever things
don‘t work out well.
The ‘water-bearing layer‘ of a lithographic printing plate consists of anodised (electrochemically
oxidised) aluminium and is porous. The printingWater
plate manufacturer determines the thickness of
Al oxide
Metal
this layer, the fineness of the grain and, as such,
Repelling the oily ink
what are known as the “dampening characteristics“ of the plate. It is these characteristics, that
the fountain solution must manage perfectly in
HH
H
H
H
the non-image areas, in order to prevent the ink
HH
O HO
O
O
from adhering to the aluminium oxide surface of
the plate. In turn, this means that no ink can be
R
R
R
R
Copying layer
transferred from the non-image areas of the plate
Al oxide
to the blanket. The diagram opposite illustrates
Metal
this principle, although it does ignore the complex
Repelling the water
processes of emulsification and interfacial surface
tension. By contrast, the fountain solution (primarily water) does not adhere (or adheres only inadequately) to the image areas of the
plate. The image areas can be inked freely and the interface between image and nonimage areas is clean.
Ink
R
Ink
R
R
R
The basis – water
Water, as it flows out of the tap, differs greatly from region to region in terms of its
make-up. It consists of the chemically defined combination of two hydrogen atoms
and one oxygen atom, plus variable amounts of dissolved substances. Among these
dissolved compounds, the majority are gases and various types of salt. Some of these
constituents of water can have negative effects on the offset printing process, while
others create conditions that need to be taken into account when adding fountain solution concentrates.
It is therefore highly advisable to analyse a number of parameters of your local tap
water. The values of some of these parameters provide information as to how suitable
the local tap water is for use in the lithographic process.
Parameter
Explanation
Target value
Total hardness in °dH
Influences the “water balance” and, when the value is very low, has been known
to cause problems with oxidative drying of inks and with printing plate surfaces.
High values are not desirable because of the risk of “stripping”.
8 - 12° dH
Carbonate hardness in mg/l
Determines how “acidic” a fountain solution concentrate has to be, so that the pH No fixed target
for the production conditions required is obtained.
value
Conductivity in µS/cm
Describes the quantity of dissolved ions in the water. If tap water is already very
highly conductive, this points to a high salt content. In individual cases, this can
lead to negative effects.
No fixed target
value
pH
The pH value is an indicator of the concentration of hydrogen ions in a liquid and
provides information as to the liquid‘s character, i.e. “acidic” or “alkaline”. Of little
importance in the case of tap water.
No fixed target
value
Halide ions, sulphates, nitrates
These are corrosive ions, which, in order to protect structural steel, should not be
present in concentrations that exceed specified values. This is particularly important in the case of dampening systems that lead to the formation of mists owing
to the character of the system (spray and centrifugal dampening systems).
< 20 mg/l nitrate
< 25 mg/l chloride
< 50 mg/l sulphate
When does water need to be treated?
In some regions, the tap water values measured fluctuate so greatly throughout
the course of the year that it is not possible to adapt to the prevailing water quality all
the time. Some water supplies are derived from different sources (e.g. lake water and
groundwater, depending on availability) and the values cited above are subject to large,
unforeseeable fluctuations several times a day. In such cases, or if one of the above limit
values is exceeded, water treatment or conditioning should be taken into consideration.
Experience shows that softening of the water followed by reverse osmosis and controlled re-hardening produces the
most reliable results.
Degrees of German hardness
0
The chart opposite shows the
German scale for the total hardness
of water compared with a common
international unit of measurement,
2
4
very soft
0
6
soft
70
too soft
8
10
12
medium hard
140
tolerable
14
16
18
1° German hardness (1°dH)
corresponds to a concentration of 10 mg
of dissolved calcium oxide (CaO) per
litre of water or 17.85 ppm. This value
reliably expresses the amount of calcium
left behind when the carrier medium,
water, evaporates. Water evaporates
readily even at room temperature.
20
fairly hard
215
22
24
28
hard
320
optimal
26
30
32
very hard
535
ppm CaO per litre
conditionally suitable
too hard
Fig. 2: German hardness scale
3
“parts per million”. Only water that falls within the green zone guarantees trouble-free
printing. If the hardness value of your tap water puts it in the white or red zone, we urgently recommend water treatment.
Softened water
with various salts
but no hardness
minerals
(calcium,
magnesium)
cation
exchange
resin
Service water
with various salts
and hardness
minerals
(calcium,
magnesium)
Fig. 3: Principle of softening
Purified
(treated)
water
(50-75%)
with approx. 3%
of all salts
Concentrate
(25-50%)
with approx. 97%
of all salts
Service
water
with various salts
and no hardness
minerals
(calcium,
magnesium)
Osmosis
membrane
Fig. 4: Principle of reverse osmosis
4
Benefits of water treatment
In practice, effects on the quality of a printed image can be observed, if fluctuations
in water hardness or other quality of the fountain solution occur. For instance, dot gain
is one factor that can experience marked effects from changes in the fountain solution.
Since, in the quest to standardise the offset process, dot gain is one of the key parameters that have to remain within certain tolerances, it is important to “standardise” the
fountain solution, too. This requires not only suitable measurement and control equipment for metering the correct quantities of fountain solution concentrate, but also a
constant quality of the employed water, i.e. tap water. The decision to install a water
treatment plant becomes unavoidable if the aim is, to achieve standardisation in accordance with the rules laid down in ISO 12647-2 to 5 and the quality of your tap water is only
conditionally suitable or fluctuates.
Hardening
Hardening refers to the adding of calcium or magnesium ions to previously treated
water. In regions with hard water, softened water can be rehardened to an appropriate
level by cutting (blending) it with untreated water. Before it is used in the offset process,
the virtually pure water derived from reverse osmosis is usually brought to the desired
residual hardness of 8 to 12° dH by adding a hardening agent.
The technologies used to treat water vary. The method, type and design of the water
treatment plant must be chosen in line with the specific purpose, requirements and
quantities of service water required. We strongly advise you to consult an expert.
Demands on fountain solution concentrates
Impact on
the water
• Setting and long-term stabilisation of the pH
• Targeted setting of the surface tension
• Partial bonding of the hardness materials
Impact in
the press
• Suitable for various dampening system models
• Protection of steel parts, rollers and plastics
• Ensuring optimum productivity
Impact on the
printing plates
• Good wetting of non-image areas
• Fast plate runoff
• Provides good corrosion protection for the printing plates
Impact on
offset inks
• Formation of a stable water-in-ink emulsion
• Fast adjustment of the ink/water balance
• No deterioration of the ink drying characteristics
Impact on
the substrate
• No partial dissolving of the paper coating
• Leaves no separating layer that could have
a negative influence on ink adhesion
All the requirements on this list are met by deploying a mix of functional, chemical
substances. The functions of the various substances can be grouped together into four
main categories:
• Buffer components ensure a stable pH of the fountain solution
• Plate protecting components remain on the non-image area after the printing
plate has dried and facilitate rapid re-dampening
• Wetting agents set the surface tension of the fountain solution and guarantee uniform wetting with a minimal amount of water
• Solubility promoters ensure that the wetting agents are miscible with the water and
that the fountain solution concentrate has an adequate shelf life
Monitoring parameters in the fountain solution
pH
0
1
2
3
4
5
6
Neutral
7
8
9
10
11
12
13
14
10-14
range favourable for printing
pH
The pH scale is used to measure
the acidity or basicity (alkalinity) of a
solution and goes from 0 to 14. The
range from 0 to 7 is defined as acidic and 7 to 14 as alkaline (or basic),
while pH 7 is neutral. Each drop in
pH of one unit means a tenfold increase in acidity.
pH (pondus hydrogenii)
Negative common (decadic) logarithm
of the concentration of hydrogen ions
The pH influences a number of
10-7
variables of relevance to the printing
-6
10
process. As the offset printing procic
10-5
cid
ly a
ess has been further developed, the
g
-4
10
sin
rea
range between pH 5.0 and 5.3 has
inc
10-3
proven to be favourable. In the USA,
10-2
however, printers frequently work
10-1
with a pH of 3.5 and still produce 100 Concentration of hydrogen ions (mol/l)
good prints. That said, the domestic
paper and ink industries there have
adapted to these low values, because the pH has a significant influence on inorganic
metal compounds in the paper coating and in the ink. Other branches of the industry
in the USA, such as newsprinting, work with neutral or slightly alkaline fountain solution
concentrates for various reasons related to the paper.
All this reveals that there is a variety of options and philosophies concerning this
matter. In Europe, however, the pH range from 5.0 to 5.3 has become established
among the manufacturers of fountain solution concentrates. With the quantity – normally expressed as a concentration (%) – of fountain solution to be added specified
and constant, this solution must set the pH to the desired range and maintain it over a
long period. For this reason, fountain solutions are buffered.
10-13
10
-12
10-11
10-10
10-9
10-8
re
inc
asi
ng
lk
ly a
alin
e
Fig. 5: pH and acid concentration
Inorganic metal compounds such
as calcium-containing constituents, can
be released from the paper coating
and cause piling or disrupt the sensitive ink/water balance. What is more,
driers in the ink are also affected. They
can lose their effectiveness and consequently retard drying of the ink.
The term buffered is used to describe
aqueous solutions whose pH does not
noticeably change when they are subjected to external influences.
5
Indicator liquids
change colour when an acid or alkali is
added. There are a number of different
indicators that change from one colour
to another at specific pH values. This
means, that a variety of different indicator
types must be used in order to measure
the pH of solutions over a wide range.
There are two methods available for measuring the pH of a fountain solution:
Indicator strips are available in many different versions and gradations. They are
simple paper strips that have been impregnated with indicator liquids that change colour and indicate the pH value on being dipped into the fountain solution. Measurement
errors of 0.5 pH units or more are frequently observed when measuring buffered or
coloured fountain systems. This method is therefore suitable only as a rough guide and
not for taking precise measurements.
Electrical measurement with the aid of a pH meter and suitable pH electrode is
extremely accurate even if the solution being measured is buffered or coloured. It is,
however, essential that the measurement equipment is stored, maintained and calibrated in accordance with specifications.
Electric conductivity
A fountain solution concentrate can only adequately satisfy the many demands
made on it if the prescribed quantity for addition is complied with. Measuring the conductivity of a fountain solution indicates how well electrical charges can be carried by
the solution. As the quantity of fountain solution concentrate in the fountain solution is
increased, the conductivity of the solution rises proportionally.
At first sight this correlation appears to make electric conductivity a perfect monitoring and control parameter; however, use of this measurement method does have its
limitations in practice, which users should be aware of and must take into account:
Conductivity in µS/cm
1500
1100
1000
650
500
1
2
Fig. 6:Differences in conductivity with
differing fountain solution chemistries
While, according to the metering instructions,
fountain solution concentrate A produces a
conductivity of 1100 µS/cm when added in a
4% concentration, concentrate B is correctly
metered (650 µS/cm) with a 3% concentration. Consequently, the conductivity value
alone cannot be taken as the basis for a
product-independent quality statement.
6
•T
hanks to its specific composition,
each particular fountain solution concentrate possesses its own range of
conductivity. Changing the fountain
solution concentrate, will usually also
lead to the conductivity of the solution
changing.
•O
wing to the fact that water also contains various salts, the electric conductivity of the fountain solution is likewise
dependent on the water quality used.
Concentrate A
Concentrate B
Fluctuations in the salinity of the water
lead to fluctuations in the conductivity
of the fountain solution.
• As you know, isopropanol is miscible
% added
3
4
5
with water in any proportion. That said,
the alcohol does not break down into
ions like the salts from the buffer system do. Isopropanol (IPA) is not capable of
transporting an electric charge and consequently, the conductivity of a fountain solution drops when alcohol is added.
• During the printing process, contaminants that get into the fountain solution can
increase (dissolved constituents from pigments or paper coating) or lower (washup
solutions, vehicles from inks) the conductivity of the solution.
• Changes in the temperature of the fountain solution alter its conductivity, even if its
composition has not been changed. The higher the temperature, the more “mobile”
the ions – and the more conductive the solution.
As long as these factors are taken into account, it does make sense to measure the
electric conductivity of the (freshly prepared) solution in order to determine how much
has been added. However, we do point out that unlike the pH value, the conductivity of
the fountain solution is not a parameter that is directly relevant to the printing process
and result.
Alcohol in the fountain solution
A very high percentage of the isopropanol used evaporates during the course of the
printing process and finds its way into the atmosphere, with negative consequences
for the environment. EU Directive 1999/13/EC on limiting the emissions of volatile organic compounds (VOCs) was aimed at reducing the solvent emissions of the member
states by 50% compared with 1990 levels by the end of October 2007 and resulted in
all branches of the chemicals industry taking a far more critical look at how they handle
technical alcohol. There are already similar and more stringent rules in other countries
around the world and in many countries, the use of isopropanol or ethanol in fountain
solution has long been banned.
The fountain solution concentrates designed for alcohol-free printing contain special active ingredients for setting the surface tension and for controlling emulsification
and transport of the solution. Alcohol substitutes are low-volatility, water-miscible substances that even in very low concentrations improve plate runoff and limit the amount
of fountain solution inks take up. They do not slow down the drying process of the inks,
nor are they harmful to health. What is more, they are suitable for use with all types of
printing plate, but can slightly shorten the service life of the plate. The products available have proven how effective they are, but are often still viewed with great scepticism.
A rethink in this regard is well overdue in some quarters!
If we restrict ourselves to reducing the concentration of isopropanol (<5%), the degree of accuracy offered by conventional alcohol metering units equipped with a float
system is inadequate. In these cases, modern, advanced systems based on other
measurement methods (e.g. infrared measurement) must be used. If we stop using
isopropanol altogether, there is no need for expensive measurement and metering systems – and add to this the savings from no longer using alcohol.
Volatile organic compounds (VOCs)
are carbon- and hydrogen-containing
substances that evaporate at low temperatures (such as room temperature)
or are present in gaseous form. There
is no globally standardised definition of
VOCs. The various definition variants
include details of the state of aggregation at the reference temperature,
the boiling range, vapour pressure,
environmental impact and/or classification of the chemical compound.
The service life of a printing plate
is measured as the number of print
images the plate can produce before
image content is lost or the quality of the
images produced drops. This manufacturer specification is often not fulfilled
if chemical or mechanical influences
destroy the surface of the plate (as a
rule, the image area) prematurely.
Corrosion protection in offset presses
A working committee set up specifically to deal with this issue drew up as long
ago as 1985 not only recommendations for anti-corrosion measures on offset presses
but also testing methods and limit values applicable to fountain solution concentrates.
These corrosion protection guidelines for offset presses – initially compiled for the
newsprinting sector – were broadened in 2001 to cover sheet-fed and web offset heatset, too. Products that conform to the requirements of this guideline are listed as certified on the Fogra website (www.fogra.org).
In addition to a suitable water quality and the use of certified fountain solution concentrates, it is also important to use corrosion-inhibited cleaning agents (washup solutions) and maintenance products.
A fountain solution concentrate is certifiable in accordance with the Anti-corrosion Guideline only if its pH is between
5.0 and 9.0 (tolerance ±0.2). In addition,
the conductivity of the service water must
increase by no more than 1700 µS/cm
for sheet-fed offset and no more than
1500 µS/cm for web offset when the
concentrate (diluted for application) is
added. Both are make-or-break criteria!
7
Microorganisms in the fountain solution
Growth constant
psychrophilic bacteria
mesophilic bacteria
1.5
1.0
0.5
2
12
22
32
42 °C
Fig. 7: Correlation between bacteria
growth and temperature
Different bacteria have different temperature
preferences. The blue curve illustrates the
growth of bacteria that love the cold, while
the red curve shows those bacteria that thrive
at 37°C. Low temperatures have a positive influence on the cell division rate of microorganisms. It should be noted that it may be more
important to ensure that there is no break in
cooling than it is to cool to a very low level.
Temperatures between 12°C and 18°C are
sufficient under normal circumstances.
Fountain solution concentrates are incapable of killing germs when diluted for application. If this were not the case, they would have to contain large quantities of preservatives, necessitating special labelling and complex disposal procedures. Since this is far
from desirable, fountain solution concentrates are set to perform the function for which
they are intended. Under favourable conditions (or unfavourable, depending on how
you see it), microorganisms can multiply between four and six times over every hour!
Cooling the fountain solution helps stabilise it in this respect, but the degree of cooling
should be chosen with a view to balancing the amount of energy (and its cost) invested
and how effective the measure is at slowing down microorganism growth. We recommend that the entire system be cleaned thoroughly every 3 to 6 months (to protect the
heat exchanger, too). If no special filtration is employed, alcohol-free fountain solution
should be used for no longer than 200 operating hours. It is essential that metering of
the fountain solution concentrate is conducted in full accordance with the manufacturers instructions, in order to ensure perfect function during production.
Metering fountain solution concentrates
If the offset printing process is to be standardised, the amount of fountain solution
concentrate to be added should also be standardised. The recommended quantity
of concentrate to be added to a product guarantees that all active ingredients are
matched perfectly to this application concentration in the necessary dosage.
Adding too much or too little concentrate is not advisable and both can lead to
problems in the long term. Corrosion inhibitors and alcohol substitutes in particular require a minimum concentration for them to develop their full effect. We recommend the
use of volumetric systems for metering purposes. The accuracy of metering systems
should be tested at regular intervals, either by means of the conductivity of the fountain
solution when freshly prepared or by means of volumetric checks. Your supplier’s technical staff will be pleased to offer you any assistance you may require.
Fountain solution waste from print shops
www.hubergroup.com
1D12/2E2
MHM Holding GmbH
Feldkirchener Str. 15
85551 Kirchheim
Germany
Owing to the fact that the fountain solution used in the offset process is completely
used up during the process, fountain solution and/or rinsing solution is/are only left
over as waste when the fountain solution system is cleaned.
From the supplier’s point of view, used fountain solution or rinsing solution currently
need to be disposed of as special waste – unless the print shop comes to some other
arrangement with the local authority.