The influence of pressure during intaglio printing on banknotes durability/Slegio itaka banknotu patvarumui spausdinant giliaspaude.
Kyrychok, T. ; Kyrychok, P. ; Havenko, S. 等
1. Introduction
Intaglio printing (gravure printing, steel engraving) is currently
an obligatory way to protect banknotes and other types of products in
majority of the world countries due to its ability to provide relief
image elements with high tactile effect (portray, inscriptions, digital
denomination, micro text) [1]. Intaglio printing machines are the
limited accessed equipment as this technology is used only for
securities manufacturing.
One of the technological peculiarities of gravure printing is high
pressure within the contact area of the plate and printing cylinders.
This causes the pressuring effect on the paper which is getting
smoother. This influencing factor being an another proof for applying
intaglio printing instead of its imitation also influences strength
features of the banknote substrate to be printed [2].
2. Analysis of intaglio printing influence on banknotes substrate
strength
During the printing nip high pressure causes specific prints of the
banknotes substrate resulting in roughing of its fibbers thus creating
calendaring effect of the intaglio printing (Fig. 1).
[FIGURE 1 OMITTED]
The Fig. 1 shows that after passing through PN nip area paper
thickness decreases from H to h resulting from the pressure P caused by
the printing cylinder. During intaglio printing high linear pressure
between the plate cylinder and printing cylinder (up to 1000 kN/m [3])
causes deforming (embossing) of the paper. Such influence is analogical
to paper calendering during its manufacturing. The pressure of the
calender rolls is significantly lower constituting 80-100 kN/m,
sometimes up to 600 kN/m [4]. Intaglio printing speed is about 8000
pages per hour [3] that taking into consideration page dimensions in
printing direction allows determining printing speed as 85-95 m/min
while calendering speed is 500-2000 m/min [4]. Thus, paper calendering
if compared to intragliopriting is characterized with lower linear loads
and shorter pressure influence applied on paper. However if we consider
that calenders comprise 10-16 rolls then the time of pressure influence
on paper during calendering and intaglio printing may be compared.
Additional wetting within 5.5-30% depending on calendering degree is
obligatory during the paper calendering. The process of intaglio
printing takes place under the conditions of paper moisture within
6.57.5% corresponding to calendering degree of writing and printing
paper [4].
High pressure caused by steel engraving influences both the
structure of the substrate and its surface thus resulting in decreasing
of paper porosity. This in its turn leads to establishing stronger bonds
between the fibers of the banknotes basis thus strengthening the
substrate.
One of the features of the intaglio printing is usage of the
viscous inks created on the basis of wax. On its way to plate cylinder
the ink temperature in gradually rising: if the temperature is kept
within 17-21[degrees]C in the ink boxes, the temperature of the chablon
rollers is about 34[degrees]C, of the collector roller is 36[degrees]C
and that of the plate cylinder is 80-82[degrees]C. Thus, heating system
of the plate cylinder melts the ink (to be more correct wax-like
compound) changing its rheological properties (decreasing viscosity and
increasing flow ability), increasing adhesion and penetration into the
structure of substrate. After printing the ink fixing occurs without
additional drying as the ink dries again thus creating mechanically
strong carcass spread throughout whole banknote surface. Besides, the
ink penetrates into the paper. The ink penetration into the paper
structure simultaneously seals the substrate providing better bonds
between the fibbers [2].
Thus, intaglio printing influences the paper structure and its
surface analogically to paper calendering during its manufacturing.
Steel engraving seals the substrate structure both by pressuring and by
ink penetration into the basis thus decreasing the banknote soiling
during its circulation and increasing its strength [2]. All these
factors lead to strengthening of the banknote substrate increasing their
durability.
3. Testing procedure
To conduct research on determining changes in banknotes
deterioration characteristics experimental samples of Ukrainian hryvnia
of 2 UAH denominations were manufactured. The technological process of
samples manufacturing included offset printing with further intaglio
printing. The samples groups differed by intaglio printing parameters
(Table 1): single sided intaglio printing with low pressure of printing
nip; normal pressure of printing nip; high pressure of printing nip as
well as double sided intaglio printing. The process of intaglio printing
was performed on "Super--Orlof--Intaglio" printing machine
with speed 85 m/min. The pressure of the printing nip during intaglio
printing was regulated by increasing and decreasing distance between
printing and plate cylinders in relation to the optimal value
established for standard banknote printing process. The minimal printing
nip pressure was the lowest level provided printing. The difference
between maximal and medium pressure was equal to the difference between
minimal and medium pressure.
Experimental samples were artificially deteriorated by means of
circulation simulator which is the device with automatic control system
of drum rotation. Circulation simulator consists of metal drum
(280x220x220 mm) with cover lid, locking clamps and rubber lining able
to rotate under certain parameters (frequency, clockwise and
counterclockwise movement).
During artificial deterioration the wearing agent as the glass
beads of two fractions (2 mm diameters (1 kg weight) and 3.3-3.8 mm (1
kg weight)) provided the multiple mechanical damages to the banknotes.
In order to increase banknotes stiffness in the wear imitation
processes the stiffening strips were fixed in left and right samples
edge. The stiffening strip is 0.5 mm thick plastic of 10 mm width cut
out in dog-bone shape with holes for fixing. To fix the stiffening
strips the Teflon weights are used.
In the course of the experiments the deterioration characteristics
of the samples before and after wet as well as dry deterioration were
analyzed. It was decided to choose as deterioration characteristics
optical (brightness, color shift), dimensional (weight, thickness)
structural (roughness, air permeability), and strength (bursting
strength, tensile elongation, Taber-type stiffness) characteristic
changes. The characteristic values were determined for the banknotes of
all the groups of samples before and after each cycle of deterioration
according to the current normative documents. After all deterioration
cycles the local damages of the samples were determined including tears
along polymer metalized strip, edge tears, dog ears. The complete list
of the characteristics is shown in Tables 2-7.
Wet deterioration of the banknotes was performed in cycles (3
cycles 10 min each) with usage of the soiling mixture modeling organic
and inorganic compounds being the basic ones during the banknotes
soiling at real circulation. The following substances were chosen for
soiling mixture:
1. Solid contaminants including white clay as an analogue of the
hygrophilous dirt with developed surface morphology;
2. Liquid contaminants including:
--sun-flower oil and olive oil used for grease substances
imitation;
--70% alcohol (ethanol) used for increasing substances containing
oxygen groups on surface and within paper substrate. Such substances
usually cause banknotes yellowing.
--artificial substance similar by its content to human perspiration
(sodium chloride (4.5 g); potassium chloride (0.3 g); ammonium chloride
(0.4 g); sodium sulfate (0.3 g); lactic acid, 80% (3.0 mg); urea (0.2
g), distilled water (1000 ml).
Dry deterioration was conducted without usage of any contaminants
within one 120 min cycle.
4. Experimental results
4.1. Banknotes characteristics changes as a result of the
deterioration imitation
As a result of deterioration imitation the following changes of
optical characteristics of the samples occur: color coordinates
difference and banknotes lightness and brightness decrease (Tables 2 and
3). The optical characteristics have been measured near water mark in
unprinted part of front side and in printed in light colors part of
reverse side of banknotes.
The increasing of thickness and mass of the paper as a result of
deterioration are especially notable after first deterioration cycle.
Air permeability and roughness increase while stiffness, bursting
strength and tensile elongation decrease (Tables 4-6). The damages of
the paper edge including tears and dog ears occur (Table 7).
Changes for all optical characteristics are less for the samples
manufactured under medium pressure values during the printing nip both
for single sided and for double sided intaglio printing.
The smallest increasing of sample thickness as a result of
deterioration was observed in case of single sided printing with low
pressure during the printing nip. This group of samples is highly
durable after dry deterioration.
However, by other characteristics the samples printed under low
pressure are the worst. Pressure increasing during intaglio printing
allows slowing down soil accumulation on the banknotes thus resulting in
thickness increase. However at the last soiling stages (3 rd
deterioration cycle) this has not been observed (Table 4).
Generally it may be seen that there is no pressure value under the
conditions of single sided intaglio printing that allows obtaining the
highest samples durability by all the characteristics. Double sided
intaglio printing provides samples with the best optical, structural and
dimensional indices and the indices of local damages but comes second
after single sided printing by the strength characteristics (Table 6).
Thus it is impossible to correctly evaluate intaglio printing parameters
influence on banknotes durability on the basis of individual
characteristics. Thereby the task to order to determine complex quality
characteristic arises [5].
4.2. Determination of the complex banknote paper quality index
Complex banknotes durability characteristic was formed as a result
of solving a multicriteria problem of choice by convolution of many
criteria to one generalized criterion creating utility function [5].
From the point of view of utility function theory the optimal solution
for the multicriteria problem of choice is the alternative with maximal
value of utility function F([x.sub.i]).
Utility function was determined by additive convolution [5] on
basis of Tables 2-7:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)
where i is the alternative number X = {[x.sub.i] | i = [bar.1,l]}
(here-types of samples (Table 1)), j is criterion number, [x.sub.ij] is
individual j criterion value for i alternative, l is alternatives
quantity (here l = 4), n is criteria quantity (here n = 33),
[[omega].sub.j] is weight of j criterion, [n.summation over (j=1)]
[[omega].sub.j] = 1, [x.sub.max j], and [x.sub.min j] are the basic
individual criteria values as maximal values for the stimulators
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and minimal values
for destimulators [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII].
Utility function (1) was formed by normalization of individual
criteria of the alternatives matrix for avoiding probable situation when
lacking value of individual utility function in relation to one
criterion may be compensated by increasing values of individual utility
function in relation to the other criterion. Besides it was taken into
consideration the separation of criteria for stimulators (to be
maximized) and destimulators (to be minimized) and destimulators
presence with basic value of [x.sub.min j] = 0:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]. (2)
It is necessary to note here that under our research the
stimulators are the bursting strength, tensile elongation and Taber
stiffness. All other criteria are the destimulators.
The Table 8 shows the values of the utility functions of the
alternatives--the types of samples obtained under different
technological modes of intaglio printing for different groups of
characteristics according to the equation (1) with supposition of equal
weight of all criteria.
Formed utility functions show that in totality of characteristics
the most durable are the samples obtained under medium pressure during
the printing nip at double side intaglio printing.
5. Conclusions
1. Durability of the experimental samples of the Ukrainian hryvnia
banknotes different by intaglio printing parameters (single side
intaglio printing with low pressure of printing nip; normal pressure of
printing nip; high pressure of printing nip as well as double side
intaglio printing) were analyzed comparing the optical, dimensional,
structural, and strength characteristic changes after wet and dry
deterioration.
2. Under the conditions of single side intaglio printing there is
no pressure value allowing obtaining the highest samples durability by
all the characteristics. Double sided intaglio printing provides samples
with the best optical, structural and dimensional indices and the
indices of local damages but comes second after single side printing by
the strength characteristics.
3. As it is impossible to correctly evaluate intaglio printing
parameters influence on banknotes durability on the basis of individual
characteristics the complex quality index was determined on basis the
utility function considering large quantity of durability
characteristics.
Utility functions obtained for every alternative (mode of intaglio
printing) allow concluding that samples printed under medium pressure of
printing nip during double side intaglio printing are the most durable
by the totality of all the characteristics. This means that double side
intaglio printing application makes it possible to increase
significantly banknotes durability
References
[1.] Van Renesse, R.L. 2005. Optical document security. Third
edition. Artech House. 368p.
[2.] Crane, T. 2011. Some observation on technological developments
in durable substrates, Int. Rev. on Cash Management 9: 9.
[3.] Kipphan, H. 2001. Handbook of Print Media. Technologies and
Production Methods. Springer. 1207p.
http://dx.doi.org/10.1007/978-3-540-29900-4.
[4.] Holik, H. 2006. Handbook of paper and board. Wiley-VCH. 505p.
http://dx.doi.org/10.1002/3527608257.
[5.] Kyrychok, T. 2013. Algorithm for solving multicriteria problem
of choice of banknote deterioration characteristics using the utility
function, Research Bulletin of National Technical University of Ukraine
Kyiv Polytechnic Institute 1: 68-75.
Received December 31, 2013
Accepted April 18, 2014
T. Kyrychok *, P. Kyrychok **, S. Havenko ***, E. Kibirkstis ****,
V. Miliunas *****
* National Technical University of Ukraine, Kyiv Polytechnic
Institute, Peremohy av. 37, 03056, Kyiv, Ukraine, E-mail:
t_kyrychok@ukrpost.ua
** National Technical University of Ukraine, Kyiv Polytechnic
Institute, Peremohy av. 37, 03056, Kyiv, Ukraine, E-mail:
vpi_ntuu_kpi@ukr.net
*** Ukrainian Academy of Printing, Podgolosko st. 19, 79020, Lvov,
Ukraine, E-mail: havenko@point.lviv.ua
**** Kaunas University of Technology, Studentu st. 56, 51424,
Kaunas, Lithuania, E-mail: edmundas.kibirkstis@ktu.lt
***** Kaunas University of Technology, Studentu st. 56, 51424,
Kaunas, Lithuania, E-mail: valdas.miliunas@ktu.l
cross ref http://dx.doi.org/10.5755/j01.mech.20.3.7393
Table 1
Samples manufacture peculiarities
Number Samples Printing nip Printing
nomination pressure
Front Reverse
side side
1 Single sided, minimal Minimal Yes No
2 Single sided, medium Medium Yes No
3 Single sided, maximal Maximal Yes No
4 Double sided, medium Medium Yes Yes
Table 2
Optical characteristics change as a result of deterioration.
Color shift
Characteristics Group Optical
Name * Color difference
[DELTA][E.sup.*.sub.ab]
(front side)
Deterioration Type Wet
Number of 1 2 3
cycles
Type of samples Single sided, 4.49 5.67 6.09
minimal
Single sided, 4.76 6.08 7.33
medium
Single sided, 4.56 5.53 6.61
maximal
Double sided, 4.73 6.01 7.12
medium
Characteristics Group Optical
Name * Color difference
[DELTA][E.sup.*.sub.ab]
(reverse side)
Deterioration Type Wet
Number of 1 2 3
cycles
Type of samples Single sided, 4.10 5.47 6.78
minimal
Single sided, 3.71 4.69 5.27
medium
Single sided, 3.90 5.82 6.30
maximal
Double sided, 3.98 4.65 5.35
medium
Table 3
Optical characteristics change as a result of deterioration
imitation. Brightness
Characteristics Group Optical
Name Brightness TAPPI
(front side), % E
Deterioration Type Wet
Number of 1 2 3
cycles
Type of samples Single sided, 9.98 11.77 14.10
minimal
Single sided, 9.19 12.48 14.77
medium
Single sided, 9.65 12.86 14.25
maximal
Double sided, 9.75 11.17 13.80
medium
Characteristics Group Optical
Name Brightness TAPPI
(reverse side), %
Deterioration Type Wet
Number of 1 2 3
cycles
Type of samples Single sided, 7.39 9.85 11.25
minimal
Single sided, 6.07 7.49 8.49
medium
Single sided, 8.04 10.21 11.77
maximal
Double sided, 6.69 7.64 9.06
medium
Table 4
Dimensional characteristics change as a result
of deterioration imitation
Characteristics Group Dimensional
Name Increased thickness, mm
Deterioration Type Wet
Number of cycles 1 2 3
Type of samples Single sided, minimal 0.007 0.008 0.008
Single sided, medium 0.009 0.008 0.012
Single sided, maximal 0.007 0.010 0.012
Double sided, medium 0.003 0.007 0.008
Characteristics Group Dimensional
Name Increased weight, %
Deterioration Type
Number of cycles 3
Type of samples Single sided, minimal 7.71
Single sided, medium 5.91
Single sided, maximal 6.93
Double sided, medium 5.08
Table 5
Structural characteristics change as a result
of deterioration imitation
Characteristics Group
Name Roughness, ml/min
Deterioration Type Wet Dry
Number of cycles 3 1
Type of samples Single sided, minimal 3486 4036
Single sided, medium 3373 4217
Single sided, maximal 3326 4239
Double sided, medium 3990 4343
Characteristics Group Structural
Name Air permeability,
ml/min
Deterioration Type Wet
Number of cycles 1 2
Type of samples Single sided, minimal 0 5
Single sided, medium 0 5
Single sided, maximal 0 5
Double sided, medium 0 0
Characteristics Group Structural
Name Air permeability,
ml/min
Deterioration Type Wet Dry
Number of cycles 3 1
Type of samples Single sided, minimal 17 201
Single sided, medium 14 243
Single sided, maximal 22 165
Double sided, medium 7 229
Table 6
Strength characteristics change as a result of
deterioration imitation
Characteristics Group Strength
Name Bursting Tensile
strength, H elongation, %
Deterioration Type Wet Dry Wet Dry
Number of 3 1 1 2
cycles
Type of samples Single sided, 47.50 32.60 9.00 5.70
minimal
Single sided, 58.15 48.40 11.40 9.00
medium
Single sided, 47.80 45.30 9.10 8.70
maximal
Double sided, 59.25 39.80 10.50 7.20
medium
Characteristics Group Strength
Name Taber-type
stiffness,
g * cm
Deterioration Type Wet Dry
Number of 3 1
cycles
Type of samples Single sided, 0.40 0.40
minimal
Single sided, 0.40 0.45
medium
Single sided, 0.40 0.40
maximal
Double sided, 0.40 0.40
medium
Table 7
Local damages as a result of deterioration imitation
Characteristics Group Local damages
Name Total length Average
of tears per length of
banknote, mm one tear, mm
Deterioration Type Dry Dry
Number of 1 1
cycles
Type of samples Single sided, 56.3 10.7
minimal
Single sided, 28.4 3.8
medium
Single sided, 63.9 16.9
maximal
Double sided, 33.8 4.4
medium
Characteristics Group Local damages
Name Total length Average quantity
of tears along of dog ears per
the polymer banknote, items
strip, mm
Deterioration Type Dry Dry
Number of 1 3
cycles
Type of samples Single sided, 14.7 2.6
minimal
Single sided, 7.9 2.6
medium
Single sided, 27.4 2.7
maximal
Double sided, 4.8 1.6
medium
Table 8
Utility functions of the alternatives--types of banknote paper
Criteria Group of Optical Dimensional Structural
characteristics
Number of criteria 12 4 7
Utility function By the groups of characteristics
Single sided, minimal 0.90 0.72 0.74
Type of Single sided, medium 0.97 0.69 0.74
samples Single sided, maximal 0.89 0.64 0.75
Double sided, medium 0.97 1.00 0.93
Criteria Group of Strength Local Total
characteristics damages
Number of criteria 6 4 33
Utility function By the groups of Complex
characteristics
Single sided, minimal 0.80 0.45 0.77
Type of Single sided, medium 1.00 0.81 0.87
samples Single sided, maximal 0.90 0.36 0.77
Double sided, medium 0.91 0.93 0.95
