Interlayer Adhesion of Coating System in Analogue and Digital Printing Technologies Formed on Lightweight Honeycomb Furniture Panels

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Do incorporate into the research porosity of the substrate, distance between the lamp and the substrate, time exposed to the curing, RH and temperature and the wet part of the lacquer.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

Thank you for taking the time to evaluate our manuscript and for your valuable comments.

1. On the page 2 in line 67: ”… types of radiators [7,11]. Do express also the moisture content which is of great importance in these cases.

Answer:

As suggested by the Reviewer, the text has been supplemented with humidity.

2. On the page 2 in line 78: ”…(W/cm2)…” It should be written (W/cm2).

Answer:

Unit notation corrected.

3. On the page 3 in line 98: ”… literature studies …” Literature citation missing upon the authors were referring with ”literature studies”.

Answer:

Due to ongoing development work on UV printing technology for furniture boards, the data provided by manufacturers is primarily of a marketing nature, without including any numerical values related to both the aesthetic-decorative characteristics and the resistance properties of the resulting lacquer coatings. Furthermore, a literature review indicates a lack of information on the adhesion properties of lacquer coatings produced in the analog/digital printing process on honeycomb boards. The bibliography in this field is limited to one position (which analyzed the impact of selected technological parameters on the topography and adhesion of UV lacquer coatings formed during the lacquering of HDF boards using roller coaters) and several others unrelated to the referenced problem. The articles listed below were prepared with our involvement.

• Tokarczyk M. Lis, B., E.-A. Salca & Krystofiak, T. (2023) Adhesion of Varnish Coatings as a Background for Analogue and Digital Printing Technologies Appl. Sci. 2024, 14(1), 304; https://doi.org/10.3390/app14010304
• Henke, M., Lis, B., & Krystofiak, T. (2022). Evaluation of Surface Roughness Parameters of HDF for Finishing under Industrial Conditions. Materials, 15(18), 6359. DOI:10.3390/ma15186359.
• Henke, M., Lis, B., & Krystofiak, T. (2022). Gloss Level of HDF Finished with Different Numbers of Layers and Hardened with UV Hg-Ga Lamps of Selected Power. Coatings, 12(4), 533. DOI: 10.3390/coatings12040533.
• Henke, M., Lis, B., & Krystofiak, T. (2023). Mechanical and Chemical Resistance of UV Coating Systems Prepared under Industrial Conditions. Materials, 16(12), 4468. DOI: 10.3390/ma16124468.
• Henke, M., Krystofiak, T., Salca, E. A., & Lis, B. (2023). Gloss Level, Type of Paper and Colour of HDF Boards Finished with the Energy-Saving Acrylic Paint System. Applied Sciences, 14(1), 394. DOI: 10.3390/app14010394
• Henke, M., Lis, B., & Krystofiak, T. (2023). Mechanical and Chemical Resistance of UV Coating Systems Prepared under Industrial Conditions Using LED Radiation. Polymers, 15(23), 4550. DOI: 10.3390/polym15234550
• Białecki, F.; Pohl, P.; Sydor, M. Investigations on sealing material consumption in relation with the roughness parameters of HDF boards. EJPAU 2008. 11., 17. http://www.ejpau.media.pl/volume11/issue4/art-17.html
• Bartoszuk, K.; Kowaluk, G. The Influence of the Content of Recycled Natural Leather Residue Particles on the Properties of High-Density Fiberboards. Materials 2023, 16, 5340. doi.org/10.3390/ma16155340

In the literature, numerous studies have been encountered concerning the adhesion of lacquer products on various substrates. These studies focused, among other things, on the impact of surface preparation methods, surface roughness, application technology, type of lacquer product, composition of lacquer products, layer thickness, number of lacquer coatings, and aging.

In this context, an experimental research project was undertaken to investigate the effect of energy dose on the adhesive properties of UV lacquer coatings formed on the surface of honeycomb boards during the printing process. This research was carried out as part of an industrial PhD in collaboration with Borne Furniture in Gorzów Wlkp. (Poland). The experimental material was prepared under the conditions of the company and subsequently tested on a laboratory scale.

4. On the page 3 in line 107: ”For the study used a lightweight cellular board …” Redefine the sentence, because it is unclear, what did the authors tried to explain.

Answer:

Done

5. On the page 4 in line 138: ”…of 40 m/min” The dot on the end of the sentence is missing.

Answer:

Added

6. On the page 5 in line 147: ”…Figure 5 …” The page layout. The Figure 5 is supposed to be on the page 4 and the same refers to the Table 2, which is supposed to be on page 6.

Answer:

Corrected

7. On the page 5 in line 164: ”Table 1 …” 95.3 ± 3, 97.6 ± 3, etc. should be written without the space between the ±, i.e. 95.3±3, … and the same goes for all the expressed numbers in the table.

Answer:

Spaces between the symbol ± have been removed.

8. On the page 7 in line 172: ”After that, …” After what does the THAT refers to? Not clear.

Answer:

The text has been completed.

9. On the page 7 in line 184: ”… 60 seconds …” Only 60 s, as it is written in the line 186 (10 s).

Answer:

Corrected

10. On the page 8 in line 214: ”The resulting systems were of high quality, with no …” Redefine the sentence, because it is unclear, what did the authors tried to explain.

Answer:

The sentence has been reworded.

11. On the page 9 in line 235: ”Table 4 …” Standard deviation should be written on only 1 decimal place and not on 2, since the mean value, min and max are expressed on 1 decimal place accuracy

Answer:

Corrected

12. On the page 10 in line 240: ”…printing creation, …” It can only be written as printouts. Printing creations does not exist as a professional term in printing science.

Answer:

In both analog and digital printing, the image formation process occurs in several stages. In the first method, the application is carried out using printing rollers, including engraved ones. The number of rollers depends on the type of pattern, with each roller applying a different shade of printing ink, and in the case of wood imitation, different elements of the anatomical structure. In digital printing, the printer prints the image on a substrate finished with layers of fillers and primers in a single-pass or multi-pass process. Considering that the printing process involves applying multiple layers of lacquer products to achieve the desired image, the authors initially used the term 'printing creation.' Based on the Reviewer's suggestion, the term 'printouts' has been used in the text.

13. On the page 10 in line 247: ”…higher contact angle, lower values (p.10, l.251), no icrease was obtained (p.10, l.259), at the highest energy (p.12, l.284), significant increase (p.12, l.284–285), the contact angle was highest at maximum does for both (p.12, l.287–288), a clear influence of the radiation (p.14, l.299–300), The highest surface free energy was (p.14, l.302), at the lowest energy (p.14, l.303), to the highest radiation does (p.14, l.305), exhibited the lowest gs value (p.14, l.305), significantly lower values compared (p.14, l.307), Greater variation (p.14, l.308–309), The highest (p.15, l.327).” In the presented results and comments, not only the comparison in high/low, etc. is sufficient. All the arguments should be expressed also with the numbers. That is why the measurements are usually performed, so that we overcome the argumentation, higher/lower, bigger/smaller, etc. What is significant?

Answer:

In accordance with the Reviewer's suggestions, the commentary on the research regarding the effect of radiation dose on the contact angle has been supplemented with numerical values.

14. On the page 10 in line 251: ”…and properties.” Porosity and the surface topography are supposed to be taken into a consideration

Answer:

We thank the reviewer for his suggestions. The following information has been added to the paper. The degree of polymerization could also have been influenced by the varying absorption of UV radiation by the lacquer products due to differences in their formulations and, consequently, their properties. In addition to its crosslinking effect, UV radiation can cause side effects such as shrinkage processes and the resulting stresses in the lacquer coatings, or changes in bond lengths. This can lead to surface variations, manifesting as irregularities or porosity in the coatings [41-45]. Structural changes in the lacquer layers may also be affected by the degree of photoinitiator migration [42]. Furthermore, there is a correlation between substrate interaction and coating roughness [46-48]. The application of successive layers alters the topography of the previously applied coating. The issue of wettability in relation to roughness has been addressed in many scientific studies [49-57]. In the present research, the base layers generally exhibited lower values of this parameter compared to the top layers, regardless of the radiation dose. This correlation could also be influenced by the aforementioned coating topography, which is also confirmed by the authors' previous work on the adhesion of coatings in analog and digital printing (Adhesion of varnish coatings as a background for analogue and digital printing technologies). This promotes interaction between the applied lacquer and the substrate or subsequent coatings. It is assumed that lacquer products better wet the surfaces, which in turn facilitates the formation of interlayer adhesive bonds [48, 59-60].

15. On the page 11 in line 275: ”…(LED + mercury lamps)…” Missing T [°C], RH [%] and a distance between the lamp and the substrate.

Answer:

In accordance with the Reviewer's suggestion, the parameters have been added.

16. On the page 14 in line 316: ”…in the table.” Missing number 6.

Answer:

Completed

17. On the page 15 in line 333: ”…In Table 7 summarized…” In Table 7 are summarized …

Answer:

Corrected

18. On the page 19 in line 393: ”…35mJ/m2…” 35mJ/m2

Answer:

Corrected

19. On the page 19 on the end: ”…Missing a conclusion on the sustainability, i.e. how does the end products influence on the sustainability of the product, since it is cured under the LED lamps

Answer:

Conclusion added

The developed printing technology on wood-based substrates represents an innovative solution that enhances consumer satisfaction not only in terms of product properties, such as adhesion, but also in aesthetics and unique designs. This technology positively impacts process stability and reproducibility, reducing costs associated with poor quality and minimizing production waste. Additionally, it aligns well with sustainable development policies by utilizing recycled materials, such as honeycomb panels and thin HDF substrates, and by reducing energy consumption through the use of LED radiators.

Additionally following papers were added to the text:

41. Park J.-W.; Shim G.-S.; Lee J.-G., Jang S.-W., Kim H.-J., Choi J.-N. Evaluation of UV Curing Properties of Mixture Systems with Differently Sized Monomers. Materials 2018, 11(4): 509. DOI: 10.3390/ma11040509
42. Nowakowski P. Badania migracji wybranych fotoinicjatorów (4-PBZ i TPO-L) z pokrytych poliakrylowymi lakierami opakowań przeznaczonych do kontaktu z żywnością. Rozprawa doktorska. Uniwersytet Marii Curie-Skłodowskiej w Lublinie. Wydział Chemii Instytut Nauk Chemicznych. Lublin, Polska, 2020.
43. Tao; Sun G.; Wei Y.; Liu R.; Zhao J. An anti-shrinkage model of an ultraviolet-curing coating filled with hollow polyurethane acrylate microspheres. Mechanics of Materials 2021, 163, 334-339. DOI: 10.1016/j.mechmat.2021.104091.
44. Zhang, H.; Feng, X.; Wu, Y.; Wu, Z. Effect of Photoinitiator Concentration and Film Thickness on the Properties of UV-Curable Self-Matting Coating for Wood-Based Panels. Forests 2023, 14, 1189. DOI: 10.3390/f14061189
45. Moeck A.; Bianchi R.; Volker P.V.; Weder R.; Helsby D, Shrinkage of UV Oligomers and Monomers. https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.radtech.org/2014proceedings/papers/technical-conference/Formulation/Moeck%2520-%2520Shrinkage%2520of%2520UV%2520Oligomers%2520and%2520Monomers.pdf&ved=2ahUKEwja6ces2YGIAxUgLBAIHczuFnQQFnoECBwQAQ&usg=AOvVaw1DkP00RyOmmEFRH7GsohiA
46. Bekhta, P.; Lis, B.; Krystofiak, T.; Bekhta, N. Surface Roughness of Varnished Wood Pre-Treated Using Sanding and Thermal Compression. Forests 2022, 13, 777. DOI: 10.3390/f13050777
47. Slabejová; Šmidriaková M. The effect of coating film thickness on the quality of surface finish on lightweight plywood. Acta Facultatis Xylologiae Zvolen 2022, 64(1), 39−58, 2022. DOI: 10.17423/afx.2022.64.1.04
48. Tokarczyk, M.; Lis, B.; Salca, E. A.; Krystofiak, T. Adhesion of Varnish Coatings as a Background for Analogue and Digital Printing Technologies. Applied Sciences 2023, 14, 304. DOI: 10.3390/app14010304
49. Pecina, H.; Paprzycki O. Lack auf Holz. Hannover, Vincentz Verlag, 1995; pp. 175.
50. Hideo N.; Ryuichi I.;   Yosuke H.;  Hiroyuki S. Effects of surface roughness on wettability. Acta Materialia 1998, 46(7), 2313-2318. DOI: 10.1016/S1359-6454(98)80012-8
51. Żenkiewicz M. Adhezja i modyfikowanie warstwy wierzchniej tworzyw wielkocząsteczkowych. Wydawnictwo Naukowo-Techniczne Warszawa, Polska, 2000; pp. 81-83.
52. Kubiak, K. J.; Wilson, M. C. T.; Mathia, T. G.; Carval, P. (2011). Wettability versus roughness of engineering surfaces. Wear 2011, 271(3-4), 523-528. DOI: 10.1016/j.wear.2010.03.029
53. Candan, Z.; Büyüksarı, U.; Korkut, S.; Unsal, O.; Çakıcıer, N. Wettability and Surface Roughness of Thermally Modified Plywood Panels. Crops Prod. 2012, 36, 434–436. DOI: 10.1016/j.indcrop.2011.10.010
54. Papp, E.; Csiha, C. Contact angle as function of surface roughness of different wood species. Surfaces and Interfaces 2017, 8, 54-59. DOI: 10.1016/j.surfin.2017.04.009
55. Yorur, H., Erer A. M., Oğuz S. "Effect of surface roughness on wettability of adhesive on wood substrates." 3^rd International Conference on Science, Ecology and Technology. Rome, Italy, 14-16 August 2017.
56. Yuningsih, I., Rahayu, I. S., Lumongga, D., Darmawan, W. Wettability and adherence of acrylic paints on long and short rotation teaks. Wood Material Science & Engineering 2019, 15(4), 229–236. DOI: 10.1080/17480272.2019.1575903
57. Bartoszuk, K.; Kowaluk, G. The Influence of the Content of Recycled Natural Leather Residue Particles on the Properties of High-Density Fiberboards. Materials 2023, 16, 5340. DOI:10.3390/ma16155340
58. Yu, Q.; Pan, X.; Yang, Z.; Zhang, L.; Cao, J. Effects of the Surface Roughness of Six Wood Species for Furniture Production on the Wettability and Bonding Quality of Coating. Forests 2023, 14, 996. DOI: 10.3390/f14050996
59. Casilla, R.C.; Chow, S.; Steiner, P.R. An immersion technique for studying wood wettability. Wood Sci Technol 1981, 15, 31–43.  DOI:10.1007/BF00366499
60. Wang, XF.; Wei, XF., Huang, PQ. Study on Performance of Adherence of Water-Base UV Varnish. Advanced Materials Research 2010, 174, 409–412. DOI:10.4028/www.scientific.net/amr.174.409

Reviewer 2 Report

Comments and Suggestions for Authors

The use of modern technologies in the creation of new products that will satisfy the consumer not only with their properties, but also with aesthetic qualities, shapes, geometry of elements and paints is an urgent task for furniture manufacturers and not only. The authors of the manuscript propose a combined use of UV products with digital or analogue printing. This is an interesting solution and, as far as I know, is already used to solve other problems.

The title is very long and I recommend shortening it.

There is no need to describe the authors' patent activity in the abstract (or which a patent has been granted...).

Figures 3, 5 do not contain scientific information and I recommend deleting it.

In Table 1, "Viscosity of delivery" should be replaced with "Viscosity" (or viscosity at a certain shear rate).

Although the manuscript I studied contains the results of the studies, I think they cannot be called unambiguously scientific. At the moment, this is a set of data that shows the observed properties (wetting or adhesion). In order for this work to become a scientific study, it is necessary to add data from structural studies to it. I don't understand what is happening with the surface morphology. How the wetting angle changes, etc. Therefore, I cannot recommend this work for publication in a scientific journal.

Author Response

Dear Reviewer,

Thank you for taking the time to evaluate our manuscript and for your valuable comments.

1. The title is very long and I recommend shortening it.

Answer:

Following the Reviewer's suggestion, the title has been shortened.

2. There is no need to describe the authors' patent activity in the abstract (or which a patent has been granted...).

Answer:

The information about the patent has been removed from the abstract.

3. Figures 3, 5 do not contain scientific information and I recommend deleting it.

Answer:

The Figures 3 and 5 have been removed.

4. In Table 1, "Viscosity of delivery" should be replaced with "Viscosity" (or viscosity at a certain shear rate).

Answer:

Changed

5. Although the manuscript I studied contains the results of the studies, I think they cannot be called unambiguously scientific. At the moment, this is a set of data that shows the observed properties (wetting or adhesion). In order for this work to become a scientific study, it is necessary to add data from structural studies to it. I don't understand what is happening with the surface morphology. How the wetting angle changes, etc. Therefore, I cannot recommend this work for publication in a scientific journal.

Answer:

We would like to address the concerns raised and clarify certain aspects of our research, which we hope will dispel doubts regarding its scientific nature.

The analog (offset) and digital CMYK printing are well-known technologies that have been used in various industries for a long time. However, the application of these technologies in combination with material finishing processes for wood-based materials using energy-saving UV radiation sources in the furniture industry is a novelty.

Our goal was to develop optimal technological processes for finishing wood-based materials in combination with digital and analog printing. The results of the conducted research have direct applications in the industry, contributing to the improvement of stability and repeatability in production processes.

First and foremost, we would like to emphasize that this type of research has not been conducted in the furniture industry before. Printing on wood-based materials is an innovative technology that is still being explored and refined, allowing for even greater consumer satisfaction not only in terms of product properties such as adhesion but also in aesthetics and unique designs. Additionally, this technology positively impacts sustainable development policies by utilizing recycled raw materials, such as cellular boards and substrates made from thin HDF panels, as well as by reducing the energy used in these processes.

In the article, we described how the changing degree of polymerisation affects the contact angle of individual coatings, which, in turn, allows for precise determination of the optimal conditions for achieving the best interlayer adhesion. The wettability of lignocellulosic materials, as well as varnish coatings, is closely related to their surface free energy, which is crucial for understanding adhesive properties.

We agree that a full morphological or structural analysis in the form of topography or roughness assessment could provide additional benefits and complement the analysis. The conducted research has demonstrated that a quick analysis of the substrate's energy state allows for appropriate adjustments in technological process parameters, leading to the optimisation of the final coating properties.

The introduction of the research methods applied in this article will help reduce costs associated with poor-quality production, which is extremely important in the industry. Proper substrate preparation allows for saving time-related to incorrect process settings. It also guides the range within which basic process parameters should be maintained, such as layer selection, application method and quantity, as well as the selection and settings of emitters. The manuscript presents systems that demonstrate the best expected results and highlights errors in process setting and parameter selection. Most of the research was dedicated to selecting optimal systems from over 120 prepared in challenging production conditions on a patented and implemented technological line by the lead author, Maciej Tokarczyk. This allowed for achieving the best expected results for both the company, which is particularly interested in expanding knowledge in this area (Borne Furniture in Gorzów Wlkp., Poland), and other entrepreneurs who wish to efficiently implement the described technologies into their processes.

The research, which mainly holds practical significance, has been validated through scientific experiments by determining the interlayer adhesion of coating systems. Based on the obtained wetting angle measurements, surface free energy, along with its dispersive and polar components, was determined. This brings a new perspective on the stability and repeatability of technological processes under industrial conditions.

We thank you for the constructive suggestions, which we will use in future scientific publications, and we believe that the introduced changes will allow our manuscript to be accepted for publication.

We would also like to note that the lead author, Maciej Tokarczyk, is conducting research under the "Implementation Doctorate" program approved by the Polish Ministry of Science and Higher Education. Due to the utilitarian aspect of the experiments conducted under industrial conditions, certain information is classified as confidential.

Once again, we thank the Reviewer for the suggestions and thorough article evaluation.

Reviewer 3 Report

Comments and Suggestions for Authors

Reviewer's comments on the paper titled “Interlayer adhesion of coating system in the analog and digital  printing technologies formed on lightweight wood-based honeycomb furniture panels with discreetly located strengthening  blocks” for the MDPI Journal Coatings (Manuscript coatings-3141533)

The paper titled “ Interlayer adhesion of coating system in the analog and digital  printing technologies formed on lightweight wood-based honeycomb furniture panels with discreetly located strengthening  blocks” is an original contribution, which corresponds to the scope of the MDPI Journal Coatings. The influence of the energy dose distributed by UV  lamps on selected parameters of varnish coatings formed during the varnishing process of lightweight cellular panels with discreetly placed reinforcing elements was investigated in the paper. The roller method in combination with digital  and analogue printing under industrial conditions was used for the boards surface finishing. The following  supplements/modifications should be done to made the current paper more clear for understanding. 

1. The title of the paper should be shortened so as now it include 18 words. Some of the additional explanations in the text of the title can be avoided.

2. Abstract of the paper should be completed by the major numerical results, obtained in course of the current investigation. This additional information will enables to understand in more details the results were obtained. Formulation “The most favorable variant”, mentioned in the line 23, should be explained in the text.

3. The following supplements should be done for the figures in the current manuscript:

·       Figure 12 should be supplied by the additional explainations of all three photos, shown on the figure (content should be explained in the designations).

·       Figure 13, 14 and 15 should be supplied by the designations and descriptions of the objects, shown on the figures. The objects can be explained in the designations below the figures.

4. Chapter 3 “Results” should be completed by the major generalizations were done basing on the results were obtained.  

5. Chapter 4 “Conclusions” should be completed by the more detailed explanation of the information, presented in the lines 396 – 403. All the stages including the layouts were mentioned, should be explained.

Author Response

Dear Reviewer,

Thank you for taking the time to evaluate our manuscript and for your valuable comments.

1. The title of the paper should be shortened so as now it include 18 words. Some of the additional explanations in the text of the title can be avoided.

Answer:

Following the Reviewer's suggestion, the title has been shortened.

2. Abstract of the paper should be completed by the major numerical results, obtained in course of the current investigation. This additional information will enables to understand in more details the results were obtained. Formulation “The most favorable variant”, mentioned in the line 23, should be explained in the text.

Answer:

As suggested by the Reviewer, the executive summary was supplemented with numerical results and an explanation of the phrase ‘The most favorable variant’.

3. The following supplements should be done for the figures in the current manuscript:

• Figure 12 should be supplied by the additional explainations of all three photos, shown on the figure (content should be explained in the designations).
• Figure 13, 14 and 15 should be supplied by the designations and descriptions of the objects, shown on the figures. The objects can be explained in the designations below the figures.

Answer:

Figures have been completed with markings and descriptions as suggested by the Reviewer.

4. Chapter 3 “Results” should be completed by the major generalizations were done basing on the results were obtained.

Answer:

In the authors' opinion, the discussion chapter includes not only specific conclusions but also general findings from the conducted research. The main generalizations identified by the authors include the following points:

In the process of analog and digital printing creation, it was found that the surface wetting process is influenced by the energy density of the radiation. At all stages of coating formation, it was observed contact angle value decreased. This correlation occurs regardless of the type of lamp used for the polymerization process. The tested lacquer systems, after exposure to mercury lamps, exhibited a higher contact angle than cured with  UV LED light.

For base layers, lower values of contact angle were recorded compared to top coats, regardless of the radiation dose.

The thickness of the finishing, which increased during the printing process, did not affect the contact angle value.

The formed layers, regardless of the energy dose delivered by the 395 nm LED emitters, were less cross-linked compared to the use of mercury lamps.

The contact angle was highest at maximum doses for both LED and mercury emitters.

As the contact angle of the analyzed coatings decreased, an increasing trend in γs values.

The γs values of the individual coatings were primarily determined by γsp.

The adhesion test results ranged from 0.5 to 0.9 MPa, although with varying types of delamination.

In the case of measurements of surface energy, such a synthetic conclusion is missing.

Taking this into account, an addition was made to the text with the conclusion that was given in the summary.

Excessive cross-linking of the surface (free energy below 35 mJ/m²) leads to adhesion problems between the substrate and the print.

5. Chapter 4 “Conclusions” should be completed by the more detailed explanation of the information, presented in the lines 396 – 403. All the stages including the layouts were mentioned, should be explained.

Answer:

Detailed explanations have been added to the various printing steps.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The answers to the questions posed have been received. However, my opinion regarding the scientific part of the manuscript remains the same.