Response to Reviewer 4 Comments

Point 1: Firstly, I would suggest adding the word *underlying* to the Title of the paper such as: The
Impact of Underlying Opaque White Coating Parameters on Flexographic Print Quality
Response 1: aceptted

Point 2: line 102: The composition of the packaging material from the research is the following: BO
PET / PEevoh / PE (Figure 1). Some slash (/) marks are missing, and EVOH is written in lowercase
letters. I believe it should be corrected to: BO/PET/PE/EVOH/PE.
Response 2: BOPET is a single-layer film and there is no need to separate it with a slash
corrected: BOPET/PE/EVOH/PE
The names of the printing substrate are now uniform in whole article

Point 3: line 161: When describing the surface energy of polymer films, it is correct to use the unit
"dyn/cm" (dynes per centimetre) instead of dynes (please correct 42 dynes to 42 dyn/cm).
Response 3: corrected

Point 4: Lines 113-116: Can you explain why EVOH film is sandwiched between two PE layers? Does
it improve the relatively poor barrier properties of PE? Is this material a functional barrier against
potential migrants from solvent-based printing inks?
Response 4: added to the article:
It is a copolymer of ethylene and vinyl alcohol, and it serves as a barrier layer. Its role is primarily to
protect the food product from the influence of oxygen and to retain the aroma and smell of the
product. EVOH is moisture sensitive and has to be combined with materials that are hydrophobic,
such as PE. In some applications of multi-layer flexible packaging, it can replace an aluminum layer.
Integrating the EVOH layer into the packaging extends the shelf life of products sensitive to external
influences. EVOH also has high mechanical strength, high resistance to oils and organic solvents, and
high thermal stability.

Point 5: At the beginning of the Materials and Methods section, you provide a description of the
experiment primarily using a schematic representation of the research process steps. Such
representation may be clear to someone in the field of graphic technology, but for researchers
unfamiliar with printing terminology and methods, it might be helpful to provide a brief additional
explanation of the process, particularly regarding the evaluation of printed samples.
Response 5: each item from the research framework is described in detail through subsequent
subsections 3.1., 3.2. and 3.3.
Chapter 3.3. Evaluation has been supplemented

Point 6: Lines 148-157: At what point the underlying white opaque ink is printed? Is everything
printed (white coating + CMYK and Pantone Red) in a single pass? Furthermore, what is the

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composition of matte varnish – is it also solvent based? How does this affect the possible invisible
set-off migration (for FCM)?
Response 6: “in a single pass” inserted in the next sentence – LINE 195
Reverse printing in a single pass is used, that is, a technique in which the ink is printed …

The composition of matte varnish is two-component, solvent-based. There is no possibility of

invisible set-off migration due to the long term cross-linking process. The main concern is that the
packaging material is wound on a reel, which only theoretically enables migration from the outside
to the inside of the packaging. This is avoided by printing on the PET material which takes place on
both sides, using ink on the inside, while the outside is matte varnished. After the printing process,
the two-component varnish needs seven days for polymerization and cross-linking under controlled
conditions. It is a norm to wait for seven days until the complete process of cross-linking the PET
material with inks and matte varnish is laminated with PE material. Therefore, there is not even an
indirect danger of transmission with regards to the migration for the food contact side with the
material. Migrations are additionally checked in certified and authorized laboratories, and the
supplier himself issues a Declaration of Conformity.

This sentence was inserted into the paper:

After the printing process, the two-component varnish needs seven days for polymerization and
cross-linking under controlled conditions to be ready for lamination.

Point 7: Lines 174-190 – can you give more explanation why you need to consider the white backing
when measuring ink opacity. And why this value isn’t included in Equation 1 - where reflectance
measured over black backing is divided with reflectance measured over white backing?
Response 7: the white backing was taken into account when measuring, i.e. it was included in final
results of measuring over-black and over-white backing (see the last figure in the series). Therefore,
two values are obtained as a result of the measurement: sample opacity percentage over black and
over white. These relative values of reflectance are then used in the calculation equation, i.e. the
spectrometer displays the final value of the sample opacity percentage. For better understanding, the
word relative has been inserted in the description of the parameters for the equation.
Below is a representation of the measurement process:

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here is what the print used in the research looked like:

Point 8: Lines 195 – 206: The DeltaECMC algorithm was used to calculate the colour difference
between the measured CIELAB values of the printed colour samples. However, for subjective
assessment metrics (Table 2), you referenced the CIE deltaE2000 algorithm instead. Since the
equations for DeltaECMC and CIE deltaE2000 are not equal and were developed by different
organizations, why didn't you use the CIE deltaE2000 equation in the first place for the evaluation of
your results? It is known that the very first version of DeltaE, DeltaE 1976, was the Euclidean distance
of colours in Lab. However, as it turned out that Lab was not as uniform in perception as once thought,
the algorithm was revised in 1984 (CMC), 1994, and finally in 2000, resulting in the most accurate and
most complicated Lab-based DeltaE algorithm to date which corresponds better with the way how
human observers perceive small colour differences.
Response 8: you are absolutely right, now it looks a bit messed up to me too
- therefore, the color difference was recalculated based on the DE2000 formula
- CMC formula was deleted, and DE2000 was added to the article
- the difference in the results is evident, and the general conclusions based on these results are
very similar to the previous ones

Point 9: I assume that the criterion stated in Table 2 (which seems to resemble the deltaE 1976
(deltaEab) algorithm rather than the DeltaE2000 equation) may not differ significantly in the
interpretation of the deltaECMC algorithm. However, it would still be necessary to provide accurate
criteria, if available. Furthermore, it would be helpful to provide a clearer definition of an acceptable
result for the printing and packaging industry in the Table 2.

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Please check following literature references for the interpretation of deltaE2000 results: Yang, Y.;
Ming, J.; Yu, N. Color Image Quality Assessment Based on CIEDE2000. Adv. Multimed. 2012, 2012,
273723 https://www.hindawi.com/journals/am/2012/273723/ and Kumar, M. Interdisciplinarnost
Barve 2.Del.; Jeler, S., Kumar, M., Eds.; Društvo koloristov Slovenije: Maribor, Slovenia, 2003; pp. 89–
100.
Response 9: thanks, a good reference that clears up any confusion about the color difference
Table 2 has been modified according to the mentioned article and now everything makes sense and
is connected in one common whole

Point 10: Lines 238-239 Can you please emphasize in the Results section what is the known acceptable
opacity of the white ink underlayer for the packaging industry when printing on flexible materials?
Response 10: perhaps it is better to mention it in the introduction - next paragraph is inserted in the
introduction chapter
Generally, the 50% white ink opacity is acceptable in flexo printing processes. Having in mind that
the white ink makes for 40–50% of total ink cost, its optimization is very important, providing there
is an acceptable level of printing quality. It is therefore important to analyze the extent to which the
increase od the white ink opacity pays off and how it influences the improvement of the visual effect
on a product. Savings in white ink expenses can significantly decrease the production costs.
Furthermore, the question arises whether an ordinary observer could even visually detect the
difference in color printed over white with higher ink opacity.

Generally, the quality of white ink in flexoprinting can be shown in 3 categories: high quality (around
70% opacity), moderate quality (around 55% opacity) and low quality (45% opacity). Print quality is
basically related to ink consumption, but as our research proves, often increasing the amount of ink
does not give adequate results, but only creates additional costs.

Point 11: In the study, you have demonstrated that a higher application of white ink results in a more
uniform layer without pinholes. However, what is the economic viability of using a larger ink volume
in practical printing? Additionally, you mention issues regarding the odour of the print and the
impact of packaging on the sensory properties of packaged food. Are there any inks available that do
not pose such issues (e.g., low migration inks)?
Response 11: There is no economic viability for a higher use of white ink. It is only for aesthetic
reasons, if we want to cover the dark content of the product so that it does not penetrate under the
white color of low opacity. Another reason could be that the colors of the design itself look fuller and

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more saturated, and third reason is to avoid possible discoloration of the product in the packaging,
due to the influence of light or some other external factors. If the packaging has gone through the
cross-linking process after printing and varnishing, and after the lamination process, there is no risk
of changing the odour of the packaging, it must be neutral and as such has no effect on the sensory
properties of the food product. The selected packaging supplier uses only low-migration inks that
have been tested and approved for the food industry.

Point 12: There are about 18% self-citations in the paper (7 out of 39 cited references), while the usual
standard allows up to 10% self-citations. Authors should consider removing unnecessary self-
citations wherever possible.
Response 12: by self-citation, we wanted to show that this article is another in a series of our long-
term research in the field of flexographic printing
self-citation was reduced to within 10% - 4 citations were left