The 14th INTERNATIONAL DAAAM
SYMPOSIUM “Intelligent Manufacturing & Automation: Focus on Reconstruction
and Development”, 22-25th October 2003
THE INFLUENCE OF PAPER ON PHYSICOCHEMICAL
CHARACTERISTIC CHANGE OF FOUNTAIN SOLUTION
Gojo, M.; Mahovic, S.; Agic, D. & Mandic, L.
Abstract: Paper with its properties
and the way of producing in the process of offset printing changes
properties of fountain solution. This is especially in respect with
newspaper paper, where of reasons of alkaline paper production process
and its composition and structure, pH value in the printing process
significantly changes. Except pH value electrical conductivity and
surface tension changes, as well other physical-chemical parameters.
Investigations in this paper covered physical-chemical measurements
of fountain solution in dependence on the quantity of newspaper printing
paper, as well interacting time of the paper to the fountain solution.
The results show that the addition of paper to the solution raises
all physical chemical parameters. The wetting process is carried out
in a mild acid media, in a pH range 4.4 to 4.9. Increasing pH value
above 6 could cause a permanent damage of bemite Al2O3 structure that
forms nonprinting elements, and that could cause changes in nonprinting
elements structure and change their hydrophility. The increase of
surface tension and contact angle of the fountain solution could cause
significant changes in physical-chemical properties. These changes
are evident in disturbing the emulgation ratio and the ink-water ratio.
Key words: contact angle, electrical conductivity,
fountain
solution, paper, pH value, surface tension
1. INTRODUCTION
The offset printing is based on various physical-chemical
properties of printing and nonprinting elements. Printing elements
must obtain hydrophobic properties and nonprinting elements hydrophilic
properties. The selective adsorption of molecular various composition
and properties are obtained. The way of paper manufacturing and in
the offset printing process changes properties of the fountain solution.
That is very expressive in newspaper printing where rather alkaline
paper changes pH value and electrical conductivity of fountain solution
during printing process. Other physical-chemical parameters could
also change, which can influence the final product.
2. BACKGROUND
Physicochemical parameters, that greatly influence the whole printing
process, are pH value electrical conductivity and surface tension.
The narrow area of pH value is caused by corrosion stability of the
bemite structure Al2O3 as the material forming the non-printing areas,
steel parts and chromium coatings on the machine parts (Pourbaix,
1966).
As already mentioned, the newspapers paper contains notable amount
of basic salts that change pH value, electrical conductivity and surface
tension. It is possible that interactions guide the offset plate surface
in unfavorable pH range where structure changes can occur and overall
properties as well.
By measuring electric conductivity, it can be obtained the increase
of electric conductive particles (anions and cathions).
Conductive particles are formed primarily by dissociation of salts
for hydrophilisation and buffer system from the fountain solution
and dissociation of dissolved salts that were extracted from the paper
that was in contact with the fountain solution as well as dissociation
of salts dissolved in water, which is used for fountain solution preparation
(Mahovic et al., 2003). Except the influence on damping of the printing
plate, pH value considerably influences the oxypolymerization, viscosity,
tackiness and tinctorial strength of the ink as well as corrosion
of the machine parts.
By measuring the surface tension of the sample, the influence of the
surface active substances from the original concentrate on the systems
of the fountain solutions as well as on the mixing and emulsification
of ink, have been observed. The basic role of the fountain solution
is the qualitative damping of the nonprinting areas.
All above mentioned physical-chemical parameters influence directly
or indirectly the damping of the printing plate (Lovrecek et al.,
1999).
3. EXPERIMENTAL
The influence of quantity of paper on electrochemical parameters
changes of fountain solution that was prepared by diluting of concentrate
by demineralised water in volume of 2.5%. Defined amount of paper
(45 gm-2) in the quantity of 0.02, 0.06 and 0.1 gcm-3 was dipped in
fountain solution. The samples of the fountain solutions were prepared
by diluting the original concentrates with the demineralised water
in concentration of 2.5% vol.
Electric conductivity of the fountain solution sample was measured
by the conductometer LF 330/SET by WTW GmbH. pH values of the sample
were measured by pH meter 330/SET from the company WTW GmbH with standard
electrode with previous calibration. Surface tension of the prepared
samples was measured by the stalagmometer method.
This comparative method measures indirectly the mass of the drop sample
in comparison with the sample of the known surface tension. The density
of the solution was measured by picnometer.
The distilled water with the surface tension 72.75x10-2 mNm-1 at 21°C
was used as the reference solution. The contact angle was measured
with goniometer NRL C.A. model N° A / 1000 with Rame-Hart. The solution
samples were measured by means of the immersing method (Dragcevic
et al., 2002).
4. MEASURING RESULTS
Measuring of mentioned physical-chemical parameters show
notable changes in comparison of parameters measured excluding the
paper influence. The increase of measured values of fountain solution
could have a negative influence on printing results.
Increase the fountain solution pH over 6 could occur a permanent damage
of Al2O3 bemite structure that form nonprinting element
(fig. 1).
The increase of electrical conductivity by particles dissolved from
the paper generates increase of surface tension and the contact angle
as well. This causes poor wetting and toning of the print that is
a negative phenomenon in the printing process.
The increase of conductivity causes increase of surface tension, that
influences inadequately or poor wetting of free surfaces (fig. 2).
Fig. 1. Dependence of the pH value and surface
tension on time.
5. DISCUSSION
Comparing the dependence of pH value and contact angle with
the paper mass it could be mentioned that additives from the paper
dissolve and increase pH value by simultaneous increasing the contact
angle. That is very visible in first fifteen to twenty minutes of
influence of paper on fountain solution. The increase of time of paper
influence on the solution the concentration of dissolve particles
rises, but there is a significant distinction between the paper quantity
and dissolved particles. The amount of paper over 0.06 gcm-3 does
not express significant increase of pH value (fig. 1) neither electric
conductivity. The reason for that fact could be building of saturated
solution, where is no further dissociation of salts present in the
paper.
Surface activants added in fountain solution cause decrease of surface
tension (Taber, 1996). The electrical conductivity depends on the
variety of ions that carry the electrical charge. So, the electrical
conductivity increase caused by conductors dissolved from the paper
increase the surface tension (fig. 1), and the increase of contact
angle as well, that result by poor wetting of free surfaces on printing
plate (fig. 2).
Fig. 2. Dependence of the pH value and cos of
the contact angle
on mass of paper.
During the wetting period the molecular layer that increase the adsorbance
of water molecules is restored by salts contained in fountain solution.
Except that salts for hydrophilisation, the surface active agents
(PAT) are added for decreasing the surface tension of water (such
as alcohol, carboxy-metile cellulose, diethyl glycol, propylene, glycerol,
etc.).
The quantity and sort of PAT additions into the fountain solution
physical and chemical properties are significantly changed. Particles
dissolved from paper could influence PAT as well added salts for hydrophilisation.
Measurements show that the breaking of pufer action can occur, and
that negative influences on the nonprinting parts of printing plate.
Increase of paper quantity in prepared fountain solutions raises all
physical-chemical parameters (except contact angle on printing elements).
The reason for that behavior is dissolving of fillers from the printing
paper, and various particles from paper manufacturing, for new and
for recycled paper as well.
Fig. 3. Dependence of the surface tension and
cos of the
contact angle on mass of paper.
6. CONCLUSIONS
The results point out that addition of paper in fountain
solution increase all physical-chemical parameters. The concentration
of dissolved particles from the paper in the fountain solution rapidly
increase in the first fifteen to twenty minutes.
The addition of paper over 0.06 gcm-3 does not show a notable change
of parameters. The reason for such behavior could be forming of saturated
solution, with no further dissociation of salts from the paper. The
wetting process take place in a slight acid media, pH ranges 4.4 to
4.9. Increasing the pH value of the fountain solution over 6 can permanently
damage the bemite structure of Al2O3 that form nonprinting elements,
and change their hydrophility.
Increasing the surface tension and contact angle in the fountain solution
could significantly change their physical and chemical properties.
Those changes take place in emulgation ratio and water-ink balance
disturbing.
7. REFERENCES
Dragcevic, K.; Gojo, M. & Agic, D. (2002). Investigations
of Physicochemical Properties of Fountain Solution in the Function
of Printing Quality Prediction, Proceedings of 13th International
DAAAM Symposium, Katalinic, B., 141-142, ISBN 3-901509-29-1, Austria,
October 2002, Daaam Int., Vienna
Lovrecek, M.; Gojo, M. & Dragcevic, K. (1999). Advances in Printing
Science and Technology, Vol. 25, United Kingdom, 1999, Pira International,
Surrey
Mahovic, S.; Dragcevic, K.; Agic, D. & Gojo, M. (2003). Paper
Influence of Electrochemical Parameters Changes of Fountain Solution,
CD, 2nd Day of Electrochemistry, pp. 59-60, ISBN 953-6894-09-2, Croatia,
June 2003, Zagreb
Pourbaix M. (1966). Atlas of Electrochemical Equilibrium in Aqueous
Solutions, Pergamon Press, Oxford, London, Paris, Toronto, New York,
Frankfurt
Traber, K. (1996). Fogra No 32., 107, Munchen
