ISSN 1846-6168 (Print), ISSN 1848-5588 (Online) Original scientific paper

ID: TG-20170816161804

THE INFLUENCE OF PRINTING SUBSTRATE PROPERTIES ON COLOR CHARACTERIZATION

IN FLEXOGRAPHY ACCORDING TO THE ISO SPECIFICATIONS

Dean VALDEC, Petar MILJKOVIĆ, Borko AUGUŠTIN

Abstract: Flexography is widely used in the packaging industry due to the fact that print can be adapted into various printing substrates, whose surface characteristics
substantially affect the reproduction quality. Accordingly, this research comprises the comparison of the most important quality parameters of graphic reproduction in accordance
with the ISO 12647-6 standard for three types of printing substrates: uncoated and coated paper and OPP film. The main goal is to examine the effect of the printing process in
combination with various printing substrates on the color characteristics on the print. After the printing of a color-test form, the characterization of prints was carried out. The
obtained results serve as the guidelines and recommendations for an easier and simpler control of reproduction. It has been concluded that the existing standard provides only
basic recommendations. Accordingly, the characterization of the process should be adjusted to the customers' expectations.

Keywords: flexography; ISO specifications; print quality; printing substrate

1 INTRODUCTION used in the process have to be mutually aligned and

optimized in order to get the best quality of the flexography
Flexography is a printing technique which uses reproduction. Therefore, all the phases of the technological
photopolymer plates with elevated printing elements that process within a unique working order have to be
leave a direct print on the substrate. The printing technique characterized, which is the basic precondition for the
is very sensitive, and the printing plate is easily adjusted to standardization of the entire process.
all printing substrates. Due to its flexibility and softness, the
substrate can cause, under pressure and low viscosity color,
an extremely high Tone Value Increase (TVI). The printing
plate makes a significant segment of the entire process
which gives the flexography certain advantages. Due to the
elastic printing elements, this printing technique enables
printing in different absorbing and non-absorbing printing
substrates such as: thin films, flexible and hard foils, all
kinds of paper, cardboard of different thickness and
strenghts, packaging material of corrugated surface and
similar [1].
The surface characteristics of the printing substrate
have a significant influece on the printing quality. On paper,
the surface is additionally enriched by the finishing
processes (coating, impregnating, parchmentization and
laminating). The most common procedure of paper finishing Figure 1 Significant influence parameters in the flexography process
is coating; therefore, the papers are divided into uncoated
(raw) and coated papers [2]. The most common and at the same time the most
The flexography process enables a high quality graphic efficient mode of achieving top print quality is coordination
reproduction which almost has a photo level quality. In the with the goal values in the ISO 12647-6 standard. However,
printing process, there have to be goal values and tolerances many printing houses set their own standards by combining
for the entire process, including the composition and ink different line screens and volumes of the anilox roller,
viscosity, plate thickness and dot consistency, the self- which in turn characterize specific printing processes in
adhering mounting tape and printing conditions (settings for accordance with specific printing substrate classes [4].
printing pressure and speed) for the consistency in
achieving the production goals [3]. 2 METHODOLOGY
The entire process of flexography consists of a large
number of influential parameters that need to be The following chapter describes the research
standardized for specific printing conditions (Fig. 1). The methodology of the influence of the printing substrate on
concept of standardizing the reproduction process includes the characteristics of colour reproduction in three types of
all the factors present in the production process which also printing substrates with the objective of comparing the
influence the quality of the final printed product. Graphic quality of reproduction and optimization of the production
prepress, printing platemaking, print and printing substrates

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process. The research framework describing the research 2.2 Printing

purpose and process is shown in Fig. 2.
The polymer plate is mounted on the plate cylinder of a
commercial, six-color flexography machine Nilpeter
FB4200. The printing is performed by the principle "roll to
roll" printing in the 60 m/min speed. In the course of the
printing process, the printing substrate passes through the
plate cylinder and impression cylinder. For an appropriate
printing pressure, the distance between the two cylinders
needs to be optimal. Light pressure is crucial for a good
quality of reproduction since it prevents the halo effect and
optimizes the Tone Value Increase [5]. It is often not easy to
print when using light pressure, namely due to the
characteristics of the printing substrate surface, the uneven
height of the printing elements or the type of task which is
Figure 2 Research framework
being printed (full color printing, combined printing or
2.1 Photopolymer platemaking process printing). Light pressure is the smallest needed
pressure for the ink to transfer from the anilox roller to the
The experimental part of this paper begins with the printing plate and from the plate to the printing substrate
design of the test form set up in a way which enables the [6].
evaluation of a quality dot reproduction by applying Printing specifications:
acceptable and established methods and research  Flexo printing machine: Nilpeter FB4200
techniques. The test form used in the experiment is shown  Flexo ink: PULSE SLM UV Process CMYK
in Fig. 3.  Printing width: 330 mm
 Printing length: 490,00 mm
 Anilox line count: 405 lpi
 Anilox cell volume: 3.1 BCM
 Printing substrate: uncoated paper, coated paper, film.

The printing experiment is envisaged in a way that the

test plate is printed by using the process CMYK UV ink on
three different printing substrates, while other parameters
are kept constant, including the speed and pressure in print,
as well as the characteristics of the self-adhesive mounting
tape and anilox roller. The chosen printing substrates are
from different quality classes with different physical and
optical characteristics (porosity, gloss, surface gloss,
opacity, grammage).
Specification of the three selected printing substrates:
Figure 3 Layout of the test form for printing  Uncoated, white, machine-finished label paper
HERMAwhite (601), grammage 72 g/m2, opacity 83%.
The color test form consists of the following elements:  White label paper, semi-gloss coated on one side
 measuring patches with cascading transition in the HERMAextracoat (242) grammage 80 g/m2, opacity
range from 0 – 100 %, 86%, surface gloss 30%.
 Ugra / Fogra test wedge for the evaluation of all the  White, high gloss, opaque OPP label film Treofan
important color-reproduction characteristics, DECOR – LWD, thickness 38 μm, unit weight 23.5
 flexo iO chart for determining the print out colour g/m2, opacity 82%, gloss 65%.
gamut,
 elements for the evaluation of the text size (from 2 – 12 Films and foils are usually defined as a thin synthetic
pt) and line thickness (from 0.05 – 0.50 mm), polymer layer. Therefore, it is necessary to prepare in
 color-image for visual print evaluation. advance the films and foils which have a significant
influence on their surface tension and enable the ink to
The photopolymer plate was made by using the LAMS connect with the printing substrate which then decreases the
digital technology with the following settings defined: line level of difficulties in printing.
screen 150 lpi, conventional AM round dot shape, screen
angles (7.5°; 37.5°; 67.5° and 82.5°) and 2540 dpi
resolution.

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2.3 Printing evaluation 3 RESULTS AND DISCUSSION

3.1 Color difference
In order to compare the research results, it is important
for the printing experiment to be set in controlled Based on the measured CIELCH values for solid patch of
conditions. Each of the chosen types of printing substrates primary CMY and secondary RGB colors on three types of
belongs to a separate qualitative group. The measured printing substrates and the goal value defined according to
CIELCH values of process colors on prints must be ISO 12647-6:2012(E) standard [8], the hue difference is
matched with the goal values according to the ISO 12647-6 calculated and compared with the acceptable deviations in
standard, i.e. within the limits of an acceptable deviation. hue color (Tab. 1). The acceptable deviation for solid tone
Densitometric and colorimetric values on printings are of the process colors according to the mentioned standard
measured by using the spectrophotometer X-Rite Exact amounts to ∆hab < 6°.
(geometry 45°/0°, standard type of lighting D50, neutral Results show that hue differences for all the process
filter (No), measuring angle 2°, aperture size 2 mm). As a colors in all three types of printing substrates are within the
result of measuring, the mean value of the three acceptable tolerances, except for the magenta in OPP films
measurements is taken in each patch for every basic print where the value of hue differences is above the upper limit
color. and amounts to ∆hab,M = 6,56°. The mean value of hue
The Tone Value Increase as the first indicator for the differences for process colors in all three types of printing
quality of reproduction is a difference between the substrates is significantly under the upper acceptable limits
measured area coverage on the print in relation to the (∆hab < 6°) and for the uncoated paper it amounts to 1,93°,
nominal value of the coresponding test patch. The Tonal for the coated paper 2,12° and for OPP film 2,73°. Such
Value Increase is never completely compensated because values indicate to precisely the opposite from the hypothesis
color reproduction will be overly light. The Controlled Tone that the highest deviations would be those in uncoated paper
Value Increase in accordance with the standard is an due to its relatively poor surface characteristics in relation
entirely acceptable occurence. to other printing substrates. Generally speaking, the
The Print Contrast, as the second examined indicator of minimal values in hue differences are seen in cyan, and
the reproduction quality, measures the ability of the printing maximal values are seen in magenta. The values in hue
process to reproduce shadow tones. The goal is to achieve a differences for secondary colors are not listed in the
larger color gamut by using the optimal color density for a calculation of average value and are shown only for
specific printing process [7]. informative purpose.

Table 1 Hue differences (∆hab) for CMY and RGB colors in line with the ISO 12647-6:2012(E) standard
DeltaH / Lch
h (ISO Uncoated paper Coated paper OPP film
12647-6) L (%) Cab (%) hab (°) ∆hab L (%) Cab (%) hab (°) ∆hab L (%) Cab (%) hab (°) ∆hab
C 233.00 58.43 46.12 234.51 1.51 53.77 61.37 231.36 1.64 56.46 62.06 233.16 0.16
M 357.00 51.74 60.69 359.47 2.47 46.18 75.63 0.17 3.17 48.47 70.28 350.44 6.56
Y 93.00 87.11 74.64 91.20 1.80 88.03 96.04 91.46 1.54 87.38 84.19 94.46 1.46
R 36.00 50.19 69.78 31.92 4.08 45.25 89.35 36.37 0.37 45.91 80.69 33.47 2.53
G 160.00 54.14 49.06 150.47 9.53 47.67 72.14 157.01 2.99 50.24 71.49 155.68 4.32
B 296.00 32.19 36.01 296.60 0.60 18.84 50.51 298.49 2.49 22.97 55.62 294.56 1.44
avgCMY = 1.93° avgCMY = 2.12° avgCMY = 2.73°

Table 2 CIE LAB values of the tested printing substrate and the recommended 3.2 Color gamut
values according to the standard
Printing substrate L* (%) a* b*
Uncoated paper 91.55 1.48 2.80 The comparison of color reproduction in the three
Coated paper 93.55 0.76 3.25 tested printing substrates is presented by the color gamut of
OPP film 91.01 0.21 −4.44 the print. Based on the measured CIELAB values of the
ISO 12647-6 >88 –3 to +3 –5 to +5 primiary and secondary colors, three hexagones were
constructed within the ab diagram that show the gamut of
According to the mentioned standard, ISO 12647-6, the the reproduced colors for a specific type of printing
recommended CIE L*a*b* values for the printing substrate substrates (Fig. 4).
are defined in the following gamut: for L* (>88), for a* The smallest color gamut was quite expectedly seen in
(from –3 to +3) and for b* (from –5 to +5). In Tab. 2, it is the uncoated paper and it is significantly smaller than in the
shown that all the examined printing substrates meet the other two types of the printing substrates. Furthermore, the
mentioned criteria. The lightness value in all printing color gamut of the coated paper is higher than in the OPP
substrates is higher than 91%. Accordingly, it was to be film, which proved to be completely opposite from the set
expected that the reproduction of the process colors would hypothesis. A larger gamut in the coated paper in relation to
be within the tolerance limits. the OPP film was seen in the red and yellow area of the ab
diagram, while in the green and blue area there are no
significant deviations. Such gamut results in the coated

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higher for 1-2% in all printing substrates than in the ISO

recommendation.

3.4 Relative printing contrast

As a rule, prints should have the highest possible

printing contrast. In order to achieve this, solid tones should
have a high color density, while the halftone screen is still
open. By increasing the ink film, the printing contrast is
increased only up to a certain limit. By further increasing
the ink film, halftone dots are filled and the printing contrast
falls down again. The optimal color density for a certain
printing process can be determined by using the relative
printing contrast based on measuring the three quarter
halftone dot patch. In the process of CMY colors, it is
measured at the 70% tone value, while for the color black it
Figure 4 Overview of the color gamut in the ab diagram for three chosen printing is measured at the 80% tone value.
substrates The obtained results for the printing contrast
indisputably show that the printing substrates with poorer
paper and OPP film can be seen in the LAB values for the
substrate characteristics result in a lower printing contrast.
printing substrates.The difference in the coordinate b (∆b)
Although unexpectedly, the highest printing contrast can be
between the mentioned printing substrates amounts to 7.69,
seen in the coated paper print (in cyan it amounts to
which indicates a shift from the blue to the yellow area of
46.20%). A significantly lower printing contrast in relation
the ab diagram (Fig. 4).
to the coated paper, for 9-13%, was measured in the
uncoated paper, while in the OPP film it is lower for 5-10%.
3.3 Tone Value Increase
This indicates that despite the better substrate characteristics
as a key parameter for the quality of reproduction, the
The printing quality in modern graphical technology is
quality parameters in the OPP film show lower values in
related to the quality of dot reproduction, and by applying
relation to the coated paper, which can also be seen in Tab.
the densitometric method, all the significant characteristics
4. Such results in the OPP film can be ascribed to the
of dot printing can be determined.
influence of surface tension between the ink and the
One of the key factors influencing the quality and
printing substrate.
accuracy of dot reproduction is the change of dot size which
can result in tone and color shifts. Therefore, the definition Table 4 Printing contrast of the process colors for the three chosen printing
of Tone Value Increase is a significant parameter in the substrates
characterization of production processes. Tab. 3 shows the Print Contrast CMY@70%, K@80%
Tone Value Increase of process colors measured in two Uncoated Coated OPP film
characteristic measuring fields (40% and 80%) for all three C 34.50 46.20 36.10
M 35.7 41.40 36.10
types of printing substrates. Tab. 3 also shows Y 26.70 40.20 30.90
recommended values in accordance with the ISO K 23.60 32.80 24.20
specifications serving as a point of comparison.
4 CONCLUSION
Table 3 Tone Value Increase in the process color for the three chosen printing
substrates
Tone Value Increase CMYK@40% / 80% The purpose of characterizing the entire reproduction
Uncoated Coated OPP label film process is in the programmed printing mode, i.e. managing
40% 80% 40% 80% 40% 80% the process from one point with a predictable and repeatable
C 22.50 10.20 21.00 11.30 20.30 13.10 quality product level. This point is a graphical prepress
M 23.30 10.40 22.20 13.10 21.60 12.10
which is connected to the overall process by the application
Y 23.60 12.60 19.40 12.00 19.20 12.90
K 24.70 10.70 21.50 11.90 22.50 13.00 of the color managing system. In the graphical prepress,
ISO 12647-6 18.2 11.0 18.2 11.0 18.2 11.0 corrections are done in certain work phases in line with the
obtained results of the specific measurable parameters of the
The Tone Value Increase results in all the tested reproduction quality. These adjustments depend on the
printing substrates show somewhat higher values from the different characteristics of the photopolymer plates,
recommended ones. The Tone Value Increase in the middle different characteristics of the printing substrates, different
tones for the process colors (at 40%) is the highest in the ink types and different anilox roller specifications. The
uncoated papers (4-6% higher than the ISO design process has to be matched with the standard, i.e. it
recommendation), while in the coated papers and OPP film, should be implemented within the framework of the
it is expectedly lower (1-2% higher than the ISO prescribed tolerances. It is therefore crucial to understand
recommendation). In shadow tones (at 80%), the values are the entire production process.

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The ISO 12647-6 standard contains in its specification geometry of pre-printed printing substrate, Tehnički
only certain values of the qualitative color reproduction vjesnik 20 (2013), 4, pp. 659-667.
parameter which serve only as a starting reference. The [7] Flexographic Technical Association (FTA),
reason behind it is that the characterization of the Flexography: Principles & Practices, New York:
production process depends on a certain combination of ink, Foundation of Flexographic Technical Association,
anilox roller, printing plates, printing substrates and printing Inc., (1999).
machine. Therefore, there are no appropriate modes of [8] ISO 2012, International standard ISO 12647-6, Graphic
implementing characterization which would take all these technology — Process control for the production of
parameters into account and define the specific values for half-tone colour separations, proofs and production
all possible combinations. Hence, it is important for the prints — Part 6: Flexographic printing, ISO, Geneva,
group of qualitative data, i.e. the process characterization, to (2012).
be aligned with the customers' expectations. The second
reason for the inability to design an appropriate standard is
the fast development of the flexographying industry and the Authors' contacts:
application of advanced technological solutions in all the
Dean VALDEC, PhD, Assistant Professor
production process areas. University North
Hue differences (∆hab) are a basic parameter in the Trg dr. Žarka Dolinara 1
process colors defined by the ISO specifications. Hue 48000 Koprivnica, Croatia
E-mail: dean.valdec@unin.hr
difference values are in this research completely matched
with the mentioned standard, which is a basic precondition Petar MILJKOVIĆ, PhD, Assistant Professor
for further characterization. Therefore, the values of the University North
qualitative parameters in the three types of printing Trg dr. Žarka Dolinara 1
48000 Koprivnica, Croatia
substrates, based on this research, can be taken as E-mail: petar.miljkovic@unin.hr
framework values in order to further specify the mentioned
production processes. Borko AUGUŠTIN
The evaluation of qualitative reproduction parameters ABS 95 d.o.o.
Jazbina 157, 10000 Zagreb, Croatia
under the influence of different printing substrate
characteristics showed significant indicators which can give
a serious contribution to the advancement of production
process and can also result in an increased quality. The
definition of repeatable and exact parameters within the
process results in a constancy of the reproduction quality.
This presents the first step towards standardization.

Note: This research was presented at the International

Conference MATRIB 2017 (29 June - 2 July 2017, Vela
Luka, Croatia).

5 REFERENCES

[1] Kipphan H., Handbook of Print Media: Technologies

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materials, tribology, recycling, MATRIB 2014, Vela
Luka, pp. 60-67, (2014).
[3] James A., Correlating anilox-roll specifications to
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(2009).
[5] Flexographic Technical Association (FTA).
Flexographic Image Reproduction Specifications and
Tolerances (FIRST) Book (3rd ed.). Ronkonkoma, NY:
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[6] Valdec, D.; Zjakić, I.; Milković, M., The influence of
variable parameters of flexographic printing on dot

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