Image Analysis Based Evaluation of Print Quality for Inkjet Printed Structures

Round 1

Reviewer 1 Report

The topic of the manuscript is of interest for the audience dealing with inkjet printing. However, the work is not dealing with wetting behavior but print quality of inkjet printing. The manuscript needs to be edited before it is ready for publishing. More detailed comments are listed in the following.

The title of the manuscript should be changed in order to have it to correspond to the work done. "wetting behavior" should be replaced with "print quality" (which is in accordance with point 3 of the work flow (line 96), and "inkjet printed electronics" should be replaced by "inkjet printed structures" (no printed electronics was studied in this work).

The general comment in the abstract about "a self-developed image analysis software including different denoising features, thresholding methods and morphology operations to differ between ink and substrate is created" is not supported by the presented data, because only one ink and one substrate was studied. For the same reason, the conclusion "It (the proposed workflow) can be easily adopted for different substrate/ink combinations and printers" is too general and is not supported by the presented, rather limited data and results. The study involves only one type of low-energetic substrate and even if it was modified by plasma treatment, no numerical values are given about how much the surface energy was modified. Therefore, for example high-energy (highly wetting) print substrates can (and most probably will) behave in a quite different manner during inkjet printing, because the ink setting (= initial adhesion (also called impact), followed by spreading wetting) may yield completely different drop size on the substrate of the injetted volume. In fact, the authors state this by themselves in the introduction in saying that "Finding suitable parameters is mostly only applicable for specific material combinations and requires many manual tests".

Yet another too general comment appears at the end of Introduction, in saying that "a simple workflow by using a self-developed image analysis tool to derive optimized surface pre-treatment and printing parameters is proposed." In this work, exactly one surface parameter was tested (plasma) and one print parameter (DS), the third parameter (substrate temperature) involves the process. For example, the ink itself was not a parameter, therefore factors such as viscosity, surface tension, density, colloidal stability (in question of a suspension as was the case here) and concentration (solids content) of the ink were not analyzed, especially the two first ones influence a lot the spreadnig wetting behavior of the ink.

Relating to the previous comment, information on the ink formulation (viscosity, surface tension, particle size etc) should be added in the Materials and Methods section. Furthermore, COC is said to have low surface energy, a value should be provided, in order to enable the reader to compare against other print substrates (speaking about generalizing the results). It would further add if surface energy values for the plasma-treated surfaces would be reported. Also, more details about the printer used should be added, including e.g. the opening (orifice) of the nozzle, essential when printing ink formulation containing particles (suspensions). Drop spacing is well described, but what was the drop size when being printed on the substrate? This information is needed when evaluating whether e.g. DS 10 corresponds to overlapping droplets.

Some more, specific issues:

Page 1, line 29: are a growig market => is a growing market

Page 1, line 34: drop-on-demand

Page 1, line 39: "the wetting behavior of the ink on", would suggest saying "ink setting"

Page 2, line 77: can be detected => were detected

Page 5, line 186: und => and

Page 6, line 200: in the caption: poor wetting => poor print quality

Page 7, line 248: could be => were

Page 8, line 264: "... underwetting can lead to function critical narrowing..." ; why do you say "can lead"? If you measured this, why not give the value?

Page 8, line 272: "... less ink needs less time to dry and therefore cannot spread to wide..."; since the sample was low-energetic, the impact (droplet coming in contact with the substrate) followed by possible spreading should rapidly find an equilibrium in wetting (corresponding to constant contact angle), therefore I don't see it motivated to claim that quicker drying would lead in less spreading, drying just simply happens quicker.

Page 9, line 300: "Higher substrate temperatures normally increase the drying and therefore the spreading of the ink"; for the same motivation as in the previous comment, I'm not convinced about the interpretation that heating would decrease spreading. In case you wanted to provide more proof for this, you should measure the diameter of the inkjetted droplet on the substrate at different temperatures.

Page 9, line 304: "With regard to underwetting, an increase in value and range can be noticed."; I think this sentence can be removed, since the sentence on line 306 gives a more exact and correct interpretation of the same thing.

Page 9, line 310: "L3 values ranges are both reduced under 120% of spreading, while L1 mean values are below 150%."; Just wondering here, what is an "acceptable" value/threshold, in the opinion of the authors?

Page 9, line 314 and forward: "While the 50°C sample exhibits a closed homogeneous surface with some overwetting effects on the track edges, the 60°C sample shows straight track edges but exhibits areas with an inhomogeneous particle distribution. These areas may still achieve some conductivity, but the whole track will not have the same resistance and the same current carrying capacity. This could be validated by an exemplary resistance measurement, which showed an about four times higher resistance for a 60°C to 50°C sample."; I think this is a very essential part of results, because here the print quality is discussed in terms of the real functionality, i.e. the resistance. I was hoping to see more results of this type, that is, numerical values on resistance and their dependence on the studied parameters. Because the optical appearance is finally of secondary importance if the resistance is low enough.

Page 11, line 335: "This article proposes a simple workflow based on image analysis to evaluate the wetting behavior in inkjet printing for different ink/substrate combinations."; Once more, results in this manuscript can not be generalized for different ink/substrate combinations. Both inks and substrates can vary a lot, thereby resulting in pronounced differences in the printability and thereby print quality.

Page 11, line 349: "...overwetting from 12.36 % (DS 10) to 5.31 % (DS 15)..."; The authors may want to consider the accuracy of overwetting, maybe one decimal would be good enough.

 

Author Response

Please see the attactment.

Author Response File: Author Response.pdf

Reviewer 2 Report

20: COC was not defined yet. Define it before 99.

119: Inkjet printing of the process used for the research should be detailed with a graphical representation.

Figure 1 components should be labeled.

157: dot after the references.

Figure 3: If you include ‘original’. The number will be five not four.

194: LCP was defined before. Do not refine. Just use LCP.

Figure 6: Hard to understand. Simplify and redo it.

Figure 7b and 10b are unclear. Closer images are required to show the red ellipses.

IQR was defined at 293. Better definition is needed since it will be used later.

 

Although 3D Printing is used in this paper. The core research is more focused on image processing and electronics. JMMP community will not have a huge interest to this research.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors did an excellent job in answering the weaknesses presented in my review.