| Abstract (english) | Processes of print varnishing are very common in the printing industry. Except for the
purpose of protection against mechanical damage of prints, and improvement of the drying
process, they are often used for improving the visual impression of a printed product.
Varnishing is applied primarily in packaging printing products, but also in the other daily used
products such as catalogs, brochures, labels, booklets. Understanding the impact of different
methods of varnishing in interdependence with the printing surface roughness on colorimetric
change of spot colors is important for the reproduction process. According to current
knowledge, the issue of change of process colors in CMYK system under the influence of
different varnishing methods is recognized, but the area of changes in spot colors remains
relatively unexplored. In this paper, emphasis is placed on the impact of the most commonly
used varnishing methods in offset printing, as well as thermal lamination processes on
frequently used spot colors, which are identified as problematic in the process of graphic
production. The research is aimed at defining the limits of colorimetric variations that may
affect the quality of the reproduction process.
To perform the research, the samples were printed in offset printing technique, according to
standardized conditions. Samples were subjected to laboratory tests of printing substrate
roughness, printing substrate gloss, and microscopic analysis. Colorimetric tests were
conducted by spectrophotometric methods in CIE L*a*b* color system. Based on the
objective, laboratory measurements and calculations were conducted, showing the extent to
which there was a colorimetric change of spot colors under the influence of various
varnishing methods and thermal lamination processes. The interdependence of printing
substrate roughness and gloss parameters was examined, and the results were placed in
correlation with colorimetric changes in colors. The border areas and conditions within which
these changes may affect the subjective experience of the average spectator - user of specific
printed products were defined. The research has yielded new scientific recommendations that
may be usable in everyday graphic reproduction and that could result in improved print
quality.
Basic concepts of the printing industry are described at the beginning of this work, as well as
other key concepts required to understand the entire process that needs to be implemented to
achieve the required research. The human experience of color, the interaction of light with thesubject that it illuminates, and the human eye as a receptor of that experience is an extremely
complicated system. As the most perfect "instrument", the human eye is able to experience
and "see" very small color differences between the printed colors, but on the other hand -
without a reference sample, the human eye "does not remember" and can easily be fooled.
Metamerism, as a phenomenon during which the human eye sees two samples the same even
though the two samples have different spectral characteristics, is an interesting phenomenon
which indicates the necessity of objective and instrumental color measurement.
In this context, the work presents the most commonly used methods of measuring color and
colorimetry that predicts colors with respect to how they are experienced by the average
observer. Colorimetric model shows the results of the same numerical values for two different
samples in cases when the average observer sees the same color. Colorimetric model shows
the different numerical values, and indicates the difference between two colors for the cases
when the average observer sees the difference between the colors.
Varnishing processes used in offset printing are diverse in terms of the effects they cause on
the printed sheets, in terms of applications, but also in terms of technical and technological
solutions which enable their application. Besides the mechanical protection achieved by
various coating processes, they are also used for improvement of visual appearance of the
printed products. Oil-based varnishes, water-based varnishes and UV varnishes are the most
commonly used varnishes for the varnishing processes. Application of oil-based varnishes
within the printing unit can be carried out by offset printing plate or directly by means of
offset printing blanket, depending on the request. Oil-based varnishes have a similar chemical
composition to the conventional offset printing inks, with the exception of pigment. Waterbased varnishing is a process that uses varnish based on water. Besides the packaging
industry, with new constructions of printing machines and increased technical and
technological capabilities, the water-based varnishes are used during the printing of other
everyday graphic products.
Water-based varnishes require a special varnishing unit, consisting of several rolls systems
and the varnish is transferred directly by a prepared coating form of a coating cylinder. The
biggest gloss effect is achieved by the process of UV varnishing, compared to oil-based
varnish and water-based varnish. Besides the in-line mode of application with the technical
and technological solutions that are part of the printing machine, UV varnishing can be
applied by a screen printing technique. Applying gloss or matte lamination with thermallamination process is one of the first stages in the process of graphic finishing. This is a very
common way of protecting printed products, used in matte or gloss version for book covers,
magazines, brochures, folders, boxes, etc. Although the lamination film seems transparent, it
still has a certain opacity and will retain a certain percentage of light that would otherwise be
reflected by the print if it has not been laminated.
For research purposes, it is necessary to consider occurrences and characteristics that occur on
the surface of the printing substrate. Interaction of printing inks, varnish and printing substrate
during the printing process significantly affects the colorimetric changes that may occur. The
roughness of the printing substrate is one of the most important factors during the process of
manufacturing paper. Printing substrate used during printing affects printing, as well as the
realization of the required reproduction, achieving gamut, trapping, drying, and subsequent
finishing processes. The various varnishing processes have different impacts on increasing or
reducing the roughness of the printing substrate. This phenomenon was observed in all three
printing substrates with respect to the experiment carried out: matte and gloss coated printing
substrates and uncoated printing substrate. Glossiness and the roughness of the printing
substrate are one of the main characteristics of the printing substrate that affects the
reproduction chain of offset printing processes and standardization of the production flow.
The various varnishing processes also influence the decrease or increase of the printing
substrate gloss. The abovementioned properties of the printing substrates can be measured in
the laboratory with special measuring equipment.
The basis of this research are spot colors that are special for several reasons. Apart from
providing the ability to increase reproduction gamut, spot colors also provide a very important
repeatability of the printing process and reproduction chain. The various systems of spot
colors used in the printing industry provide a variety of applications and benefits. One of the
most commonly used system of spot colors in the printing industry is Pantone® color system.
During the printing process, spot colors show a number of characteristics, which is important
to recognize and understand in order to achieve a satisfactory reproduction process.
Colorimetric change of spot colors can be influenced by numerous parameters, including the
various varnishing methods and laminating processes. The change of printed color is not
necessarily immediately visible during printing, but it can also occur in a certain period of
drying time, and even after a few weeks.Eight spot colors of contrasting wavelengths were selected for the implementation of the
experiment. Samples were printed in standardized conditions in offset printing technique. The
printed colors were subjected to various varnishing processes and a thermal lamination
process. During the process of printing samples, part of prints remained uncoated, and the
second part of the prints was coated with oil-based varnish in matte and gloss version, waterbased varnish in matte and gloss version, and UV gloss varnish, also under controlled
conditions. Laboratory tests determined the parameters of roughness and gloss of the printed
samples. Upon completion of samples, calculations were conducted that showed the extent to
which there was a colorimetric change of spot colors, as well as to determine the
interdependence of roughness and gloss properties of the printing substrate. Measurement of
paper smoothness was carried out according to Bekk method. This exact method is based on
the air flow between the paper and the smooth surface. Elcometer 407 was used for measuring
the gloss of the printing substrate, which enables the measurement of three angles: 20°, 60°
and 85°. Spectrophotometric measurements in the CIE L*a*b* color system were used for the
purpose of defining and calculating colorimetric tolerances.
The results of smoothness measurements showed that the greatest smoothness was achieved
on samples with lamination. After that, the highest values were achieved on the samples with
water-based gloss varnish, and then oil-based gloss varnish. Water-based matte varnish and
oil-based matte varnish on matte and gloss coated printing substrates resulted in the reduction
of surface smoothness relative to samples without varnish. Gloss and matte coated printing
substrates reacted similarly influenced by different types of varnishing and laminating
processes. On uncoated printing substrate, various types of varnishes, in contrast to gloss and
matte thermal lamination processes, did not cause significant change in the surface roughness.
Results of gloss measurement showed that various varnishing methods did not largely
influence the change in glossiness of the samples printed on uncoated printing substrates.
Initially, large surface roughness of uncoated printing substrate was not significantly changed
by the application of coating, and therefore, the glossiness of the surface slightly changed in
relation to the sample without varnish. On the gloss coated printing substrate, various
varnishing methods significantly altered the gloss of the printing substrate. Different types of
varnishing and lamination caused almost the same changes on the gloss coated printing
substrates as on the matte coated printing substrates. For all measured samples, UV gloss
varnish, and then water-based gloss varnish, caused the largest increase in gloss.Measurements of gloss and roughness of the printed samples confirmed the interdependence
of these two parameters.
In order to determine changes in the CIE L*a*b* values that different laminating and various
varnishing methods caused to the individual samples, after the visual presentation of changes
through 3D graphs, tabular calculation were made, and the overall results were presented for
all printed samples. It is necessary to take into consideration that all the changes in which
∆E00 * > 2 are treated as changes that are visible to the average observer, and as such influence
and/or may affect the quality and impression of finished printed products.
The spectrophotometric measurement of color PANTONE Rubine Red showed that for all
three types of printing substrate, it is common that at low values of raster tone (20 %)
combined with a matte or gloss lamination process, and UV gloss varnish resulted in
significant ∆E00 * > 3. In the field of medium raster tone values (50 % and 80 %), matte and
gloss lamination, as well as UV gloss varnish, caused ∆E00 * > 3. With 100 % raster tone value,
except for laminating, the color change is affected by both matte and gloss water-based
varnishes.
The spectrophotometric measurement of color PANTONE Warm Red showed that for all
three types of printing substrate, it is common that at low values of raster tone (20 %)
combined with a matte or gloss lamination process, and UV gloss varnish resulted in
significant ∆E00 * > 3. In the field of medium raster tone values (50 %), matte and gloss
lamination, as well as UV gloss varnish, caused ∆E00 * > 3. With 100 % raster tone value on
matte and gloss printing substrates, ∆E00 * > 2 was noticed only under the influence of matte
lamination process.
The spectrophotometric measurement of color PANTONE Orange 021 showed that for all
three types of printing substrate, it is common that at low values of raster tone (20 %)
combined with a matte or gloss lamination process, and UV gloss varnish resulted in
significant ∆E00 * > 3. This is especially visible on both matte and gloss coated printing
substrates. In the field of medium raster tone values (50 %), gloss lamination, as well as UV
gloss varnish, caused ∆E00 * > 3. At 80 % raster tone value, water-based matte varnish caused
∆E00 * > 2 on matte and gloss coated printing substrates. With 100 % raster tone value on matte
and gloss coated printing substrates, ∆E00 * > 3 was noticed only under the influence of matte
lamination process and water-based matte varnish.The spectrophotometric measurement of color PANTONE Yellow showed that for all three
types of printing substrate, it is common that at low values of raster tone (20 %) combined
with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * >
3. In the field of medium raster tone values (50 %), matte and gloss lamination, as well as UV
gloss varnish caused ∆E00 * > 3 on matte and gloss coated printing substrate, while on uncoated
printing substrate caused ∆E00 * > 2. ∆E00 * > 2 changes were not noticed while measuring on
matte and gloss coated printing substrate on 80 % and 100 % raster tone value. On uncoated
printing substrate at 80 % and 100 % raster tone value, only the process of gloss lamination
caused ∆E00 * > 2.
The spectrophotometric measurement of color PANTONE Green showed that for all three
types of printing substrate, it is common that at low values of raster tone (20 %) combined
with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * >
3. An exception to the above represents matte coated printing substrate in combination with a
matte lamination process. In the field of medium raster tone values (50 %), matte and gloss
lamination, as well as UV gloss varnish, caused ∆E00 * > 3. With 100 % raster tone value on
matte and gloss coated printing substrates, ∆E00 * > 2 was noticed only under the influence of
matte lamination process.
The spectrophotometric measurement of color PANTONE Reflex Blue showed that for all
three types of printing substrate, it is common that at low values of raster tone (20 %)
combined with a matte or gloss lamination process, and UV gloss varnish resulted in
significant ∆E00 * > 3. With 100 % raster tone value on matte and gloss coated printing
substrates, ∆E00 * > 3 was noticed only under the influence of matte lamination process and
water-based matte varnish. Almost all methods of varnishing caused ∆E00 * > 2 on an uncoated
printing substrate in certain situations.
The spectrophotometric measurement of color PANTONE Violet showed that for all three
types of printing substrate, it is common that at low values of raster tone (20 %) combined
with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * >
3. With 100 % raster tone value on matte and gloss coated printing substrates, ∆E00 * > 3 was
noticed only under the influence of matte lamination process and water-based matte varnish.
On uncoated printing substrate at 100 % raster tone value, ∆E00 * > 2 was not measured only on
the samples with oil-based matte and gloss varnish.The spectrophotometric measurement of color PANTONE Purple showed that for all three
types of printing substrate, it is common that at low values of raster tone (20 %) combined
with a matte or gloss lamination process, and UV gloss varnish resulted in significant ∆E00 * >
3. With 100 % raster tone value on matte and gloss coated printing substrates, ∆E00 * > 2 was
noticed under the influence of matte lamination process. Water-based matte varnish on matte
and gloss coated printing substrates also caused ∆E00 * > 2. On the matte coated printing
substrate ∆E00 * > 2 was also caused by matte and gloss oil-based varnish.
Considering all of the observed colors on uncoated printing substrate, under the influence of
various varnishing methods and laminating processes, the most sensitive was PANTONE
Violet, in which 79 % of the samples had ∆E00 * > 2 changes. After PANTONE Violet,
PANTONE Reflex Blue followed with 68 % and PANTONE Rubine Red with 50 % of the
samples that had changes ∆E00 * > 2.
Considering all of the observed colors on matte coated printing substrate, under the influence
of various varnishing methods and laminating processes, the most sensitive was PANTONE
Purple, in which 49 % of the samples had ∆E00 * > 2 changes.
PANTONE Reflex Blue and PANTONE Rubine Red followed with 39 % of the samples that
had changes ∆E00 * > 2.
Considering all of the observed colors on gloss coated printing substrate, the most sensitive
was PANTONE Reflex Blue, PANTONE Violet and PANTONE Rubine Red in which 39 %
of the samples had ∆E00 * > 2 changes. The smallest changes, as with an uncoated and matte
coated printing substrate, occurred on PANTONE Green and PANTONE Yellow.
Results presented in this research can be used as recommendations for achieving optimum
results when printing spot colors in combination with the most commonly used varnishing
methods and thermal processes, and on conventional printing substrates. |
