1. International Journal of Graphics and Multimedia (IJGM),
0976 – 6448(Print),
INTERNATIONAL JOURNALDecember ISSN © IAEME AND
OF GRAPHICS
ISSN 0976 – 6456(Online) Volume 4, Issue 2, May 2013,
MULTIMEDIA (IJGM)
ISSN 0976 - 6448 (Print)
ISSN 0976 -6456 (Online)
Volume 4, Issue 2, May - December 2013, pp. 11-19
© IAEME: www.iaeme.com/ijgm.asp
Journal Impact Factor (2013): 4.1089 (Calculated by GISI)
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IJGM
©IAEME
IMPROVEMENT OF (ИЛИ IMPROVING THE) COLOR
REPRODUCTION ACCURACY OF FLEXO PRINTING
TECHNOLOGY FOR DIFFERENT PRINTING SUBSTRATES
TATYANA BOZHKOVA, TANYA STEFANOVA, ALEXANDER GANTCHEV
University of Chemical Technology and Metallurgy, 8, St. Kliment Ohridski Blvd.,
1756, Sofia, Bulgaria
ABSTRACT
Analysis of color shift for spot colors and specification of the lowest color difference
on client’s samples in flexo printing on various printing substrates is carried out. The
analyses are based on two main stages. The first stage is focused on a laboratory research,
and based on it are selected the specifications of anilox rollers. The goal is to invest less time,
cut production costs and diminish the hazardous impact on the environment by reducing
waste. The second stage spreads over the complete preparation of the printing press and
results in a real printing process. An additional task is to analyze if the results received in the
lab will be confirmed in a real production conditions.
Keywords: Color Differences, Flexo Printing, Printing Presses, Optimization of Printing
Conditions, Inks for Flexo Printing and Color Reproduction.
INTRODUCTION
With the appearance of writing, as a tool to reflect human thoughts, arose the
necessity to protect knowledge. With time passing, the need not only to protect the
information, but also to make it available for more people appears strongly. This accelerates
the development of methods for reproduction of the available information. The development
in graphic arts is in the direction of satisfying the need to reproduce information. Printing is
an important branch of the industry, which is serving the different needs of the cultural,
economic and political life of society. The printing industry includes production of books,
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2. International Journal of Graphics and Multimedia (IJGM), ISSN 0976 – 6448(Print),
ISSN 0976 – 6456(Online) Volume 4, Issue 2, May - December 2013, © IAEME
newspapers, magazines, brochures, catalogues, packaging and many others, but the
requirements for color consistency in the printing process is different. Various printing
methods are developed to reproduce identical copies on many various materials with flat or
relief forms. There are different printing methods, such as letter press, litho offset, gravure,
screen or digital printing, with a lot of varieties [1]. What is very important when talking
about packaging is the color consistency, especially when we are focused on the printing of
spot colors for different registered trademarks of print buyers. During the years, all these
methods have been developed and improved, with the goal to increase their quality and
reliability, while in the same time reduce the hazardous impact on the environment. In
parallel to the new development of printing technologies, there are more and more advance
methods to control the process [2, 3, 4], which lead to the optimization of the printing process
and predictable and repeatable results as well, especially in colors [ 5, 6, 7 ].
EXPERIMENTAL
Web flexo printing press MPS Systems bv
Maximum printing width - 410 cm.
Number of colors - 8 nb.
UV – driers – 8 nb.
The printing process for the experiment was at fixed printing speed and tension of the
print substrate.
Ink
For the test trial Pantone 354 ink was used. The ink is mixed according to the given
ink formulation and contains no solvents. It is appropriate for UV-drying inks and for the
used substrate.
Print substrate
Fasson MC Primecoat S 2000 N (self-adhesive papir)
HGW (self adhesive paper - glossy)
PE on a self-adhesive paper.
Anilox rollers
Anilox rollers, with characteristics shown in Table 1, were used for the test trial, as
these are used the most in the printing house.
Used tapes and test targets
In the research two different type of adhesive tapes were used – soft and hard, and two
kinds of solid areas were tested – solids 100% and screened solids of 98%.
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3. International Journal of Graphics and Multimedia (IJGM), ISSN 0976 – 6448(Print),
ISSN 0976 – 6456(Online) Volume 4, Issue 2, May - December 2013, © IAEME
Table 1: Anilox rollers with different volumes used in the research
Ink volume [сm3/m2]
5.5
6.5
7.5
10
Screen ruling of the
anylox rollers [lpi]
800
800
750
250
RESULTS AND DISCUSSION
The analyses are carried out on two basic stages. The first stage is focused on a
laboratory research, used to specify the anilox rollers. The goal is to use less time, resources,
as well as to reduce the impact on the environment, and to check if the results achieved in lab
conditions will correspond to the real printing process. The second stage includes the entire
preparation of the printing press and printing the samples in working conditions.
Laboratory investigations
The spot color is prepared by mixing two colors, in accordance with the ink
formulation for Pantone. Then tests are printed on a proofing press Orange Proofer. Four
different screen rulings and three different aniloxes with different ink volumes were used.
Samples are printed for each combination, as the samples are chosen according to a
preliminary defined model and each tenth sample is accepted as a specimen and is measured
with a spectrophotometer. The next step is evaluation of the print tests. The values for the
color differences for the different substrates are shown on Table 2 and Figure 1. The color
differences were calculated according the following formula:
∆Eab= {∆a2+∆b2+∆£2}½
Where:
∆£= £1 - £2 (£1 - coordinates of the unknown color, £2 - coordinates of the real color)
∆a = a1 - a2 (a1 - coordinates of the unknown color, a2 - coordinates of the real color)
∆b = b1 – b2 (b1 - coordinates of the unknown color, b2 - coordinates of the real color)
Lab tests show that the best results are achieved with anilox rollers with volume 6
cm3/m2,and when “Top white” was used as a print substrate.
Table 2: Color differences of print samples printed on Orange Proofer
Anilox volume
[сm3/m2 ]
5
6
7
10
∆Eab 100% of
Top white
7
3.13
4.49
8.46
∆Eab100% of
Primecoat
15.18
14.17
14.26
14.53
∆Eab 100% of
HGW
10.32
6.3
8.32
8.05
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4. International Journal of Graphics and Multimedia (IJGM), ISSN 0976 – 6448(Print),
ISSN 0976 – 6456(Online) Volume 4, Issue 2, May - December 2013, © IAEME
Figure 1: Comparison of color differences for three kind of substrates, printed at the same
conditions with pantone 345 ink
RESEARCHES IN WORKING PRINTING CONDITIONS
During the second stage, test trials were done at the operational parameters used in
daily working conditions. During this stage of the test trials, two different tapes were used,
soft and hard, in addition to the different aniloxes and test images,. Different combinations
are shown in Table 3.
Table 3: Materials and equipment used in the experiment
Anilox
volume
Substrate
5.5
cm3/m2
800lpi;
SB
6.5
cm3/m2
800 lpi;
SB
7.5
cm3/m2
750lpi;
SB
10.00
cm3/m2
250lpi;
SB
5.5
cm3/m2
6.5
cm3/m2
800lpi;
HB
7.5
cm3/m2
750lpi;
HB
10.00
cm3/m2
250lpi;
HB
Fasson
MC
Primec
oat
Fasson
MC
Primec
oat
Fasson
MC
Primec
oat
MC
Primec
oat
Fasson
MC
Primec
oat
Fasson
MC
Primec
oat
Fasson
MC
Primec
oat
MC
Primec
oat
PE top
white
PE top
white
PE top
white
PE top
white
PE top
white
PE top
white
PE top
white
PE top
white
HGW
HGW
HGW
HGW
HGW
HGW
HGW
HGW
14
800lpi;
HB

5. International Journal of Graphics and Multimedia (IJGM), ISSN 0976 – 6448(Print),
ISSN 0976 – 6456(Online) Volume 4, Issue 2, May - December 2013, © IAEME
The color shift and the color differences ∆Еab are measured after printing all samples
and careful selection.
The samples are selected according to a preliminary defined model, as each tenth
sample is selected as a specimen and 10 samples from each combination are selected (for a
combination of a substrate – anilox roller – tape). ∆Еab is measured for 100 % and for 98 %
screened solids and the results of the average ∆Еab are shown in Table 4.
Table 4: Average ∆Еab for different print conditions
Anilox
volume
5 cm3/m2
6 cm3/m2
7 cm3/m2
10 cm3/m2
Form
SB
HB
SB
HB
SB
HB
SB
HB
Top white –
∆Еab, 100%
2.00
1.86
2.13
1.70
5.23
6.49
12.15
13.42
Primecoat –
∆Еab, 100%
4.79
5.51
5.14
3.85
6.20
6.73
13.23
13.40
HGW –
∆Еab, 100%
2.26
2.05
1.77
2.07
7.17
7.53
14.20
14.61
Top white –
∆Е, 98%
2,30
1,45
1,67
1,67
6,02
7,2
13,11
13,31
Primecoat –
∆Еab, 98%
3.81
4.42
3.98
4.02
6.65
7.14
13.94
13.95
HGW –
∆Еab, 98%
3.73
3.58
2.53
2.53
8.35
8.20
14.70
14.41
The measured ∆Еab and the average color differences achieved during test trials are
shown in Fig. 2 and 3.
The analyses show that the results achieved in the laboratory conditions are confirmed
and correspond to what was expected. Therefore, that they may be used to preliminary define
the values for real working conditions. With the help of the laboratory data, the waste
materials and the working time are significantly reduced and lead to optimization of the
production process.
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6. International Journal of Graphics and Multimedia (IJGM), ISSN 0976 – 6448(Print),
ISSN 0976 – 6456(Online) Volume 4, Issue 2, May - December 2013, © IAEME
Figure 2: Comparison of ∆Еab for the three kinds substrate with the use of soft tape
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7. International Journal of Graphics and Multimedia (IJGM), ISSN 0976 – 6448(Print),
ISSN 0976 – 6456(Online) Volume 4, Issue 2, May - December 2013, © IAEME
Figure 3: Comparison of ∆Еab for the three kinds of substrates with the use of hard tape
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8. International Journal of Graphics and Multimedia (IJGM), ISSN 0976 – 6448(Print),
ISSN 0976 – 6456(Online) Volume 4, Issue 2, May - December 2013, © IAEME
CONCLUSIONS
Based on the test trials and print samples evaluations, the following conclusion may
be given for the tested Pantone 354 ink with flexo printing of client’s samples for defining the
smallest color differences:
For the “Top white” substrate – the results received in the lab show that the use of
anilox rollers with volume of 5 cm3/m2 is recommended. When the real printing process is
used, it is confirmed that those with 5 cm3/m2 are the most suitable. The differences in ∆Еab
at both aniloxes are insignificant. It is observed that at 98% tone value and anilox 6,5
cm3/m2, the values of ∆Еab for both hard and soft tapes are approximately the same.
According to the results, the lowest ∆Еab is achieved at 98% tone value and 5, 5 cm3/m2
volume aniloxes.
At “Primecoat” substrate - the results from the lab show that none of the anilox
rollers is suitable for this job. In all four cases the value of ∆Е surpasses the recommended
values. The laboratory results are confirmed during real printing. Regardless of the used
combination, the lowest values for ∆Е are in the range of 3,80, which means that such color
shift will be visible by a naked eye. Such color difference is not an exception for spot colors,
but it exceeds the requirements of critical print buyers.
For “HGW” substrate – when using HGW in lab conditions, the results are, in general,
acceptable for the color difference with anilox volume of 6 cm3/m2. Real printing process
shows good results for ∆Еab when using 6,5 cm3/m2 anilox volume and 100% solid tone. The
color difference increases at 98% tone value. Increase of ∆Еab is observed when hard tape is
used and that is why the use of soft tape is recommended.
From all conclusions listed above, it can be summarized that the best results are
achieved with РЕ Top white substrate. The color differences received with the Primecoat
substrate prove in practice that good color reproduction is difficult. At HGW good color
reproduction may be achieved by using aniloxes with volume 6, 5 cm3/m2 and 98% tone
value. Here, the tape does not have a significant influence on the print results.
REFERENCES
1. H.Toliver-Nigro, “Printing technologies”, Moscow, 2006.
2. E. Petkova, I. Spiridonov, I. Lozanova-Doncheva, R. Boeva-Spiridonova, ”Investigation of
thermal ageing and influence of conservation treatment on colour characteristics and
physical and mechanical properties of offset imprints on glossy coated paper”, 5th
International GRID symposium,11-12 November, Novi Sad, Serbia, 2010. pp 39-44.
3. I. Spiridonov, “Comparison of Optimal Inking Obtained by Using the Method of
Maximum Print Contrast and Inking Obtained by Achieving the Color Values in CIE
LAB”, 42nd Conference of the International Circle of Educational Institutes for Graphic
Arts Technology and Management,19-20 October, Moscow, 2010, pp133-138.
4. I.Spiridonov, N.Kachin, “Determination of the Deviations Tolerances of the ProcessColour Solids from the OK Print in Offset Printing Method”, 42nd Conference of the
International Circle of Educational Institutes for Graphic Arts Technology and
Management, 19-20 October, Moscow, 2010, pp138-145.
5. Helmut Kipphan,. “Hanbook of Print Media”, Springer, Germany, 2001, pp214-460.
6. R. Piers, “Handbook of printing inks”, Springer, 1993.
7. ISO 12647 – 6, 2004, Graphic technology.
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9. International Journal of Graphics and Multimedia (IJGM), ISSN 0976 – 6448(Print),
ISSN 0976 – 6456(Online) Volume 4, Issue 2, May - December 2013, © IAEME
INFORMATION ABOUT THE AUTHORS
Dr. Tatyana Bozhkova is working for the University of Chemical Technology and
Metallurgy Sofia, Bulgaria, as an assoc. professor of Department of Printing Arts, Pulp and
Paper.
Ing. Alexander Gantchev is working for the University of Chemical Technology and
Metallurgy Sofia, Bulgaria, as an assistant of Department of Printing Arts, Pulp and Paper.
Mrs. Tanya Stefanova is a student in the University of Chemical Technology and
Metallurgy Sofia, Bulgaria, as an assistant of Department of Printing Arts, Pulp and Paper
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