# New Flexible Protective Coating for Printed Smart Textiles
## 2 Materials and Methods
### Printing Process
#### 2.3.3 Screen-Printing Technology  
Protective layers as well as the conductive structure were applied by screen-printing. For this, we used a Schenk Variprint Easy screen-printing carousel with three different print stations equipped with a polyester mesh 32-100 PW and 8 aluminum pallets  
The screen-printing process first consists of a flooding step followed by a printing step. During the flood stroke, the lifted mesh of the stencil is filled with paste without being in contact with the substrate. During the printing stroke, the paste in the screen is then transferred to the substrate. This process makes it possible to print an exactly defined amount of paste on a textile.  
Before printing the whole protected conductive structure, we determined the optimum print parameters for the protective layers using a response surface method experimental design. Because both protective polymer dispersions had a similar rheological behavior, only the flexible paste was used to determine the print parameters. To limit the number of tests, the following printing parameters were fixed on the basis of existing preliminary tests and experience [25; 26; 27]:  
- Flood bar angle: Usually, a squeeee angle of 75\({}^{\circ}\) is used.  
- Squeeze pressure during flooding: 1.5 bar.  
- Flooding speed: 10 mm/s.  
- Flood bar type: aluminum.  
- Printed paste: paste for the flexible layer. All the protective pastes have a similar viscosity. It is expected that the parameters determined for the flexible layer can also be applied to the diffusion-inhibiting paste.  
- The influence of the following parameters on the printing process was investigated:  
- Off-contact distance: 2-6 mm. A jump of 2 mm ensures that the screen fabric does not come into contact with the substrate during flooding. For jumps larger than 6 mm, very high squeeee pressures are required to bring the screen fabric into contact with the substrate during printing. This could damage the screen fabric.  
- Squeeze hardness: 80 Shore (hard), 60 Shore (soft). Squeeze hardness influences the amount of paste applied to the substrate. A soft squeeee usually applies more paste.  
- Squeeze pressure during printing: kissing-print + 0-0.5 bar. The kissing-print corresponds to the pressure required for punctual contact of the screen fabric with the substrate. This pressure is highly dependent on the off-contact distance (Table 2). Therefore, only the additional pressure to the kissing-print was considered in the experimental design.  
- Squeeze speed during printing: 10-30 mm/s. The speed of the printing squeeee influences the amount of material applied to the substrate and the print quality, among other things.  
The paste quantity, the homogeneity of the layers and the print quality (complete print) were defined as target values and were optically evaluated in order to determine the quality of the samples. A statistically significant model was created for each target figure. A total of 40 trials were carried out to determine the print parameters.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Off-Contact Distance (mm)** & **2** & **3** & **4** & **6** \\ \hline Kissing-print-pressure (Bar) & 1.5 & 1.6 & 1.7 & 1.8 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Dependence between the off-contact distance and the kissing-print pressure.