Transfer decal process

As we discussed above, there are two major types of CL fabrication techniques. One is to apply the catalyst ink onto the gas diffusion layer to form a catalyzed diffusion medium (CDM), and the other is to apply the catalyst ink onto the PEM to form a CCM. Normally, applying the ink to the gas diffusion medium has the advantage of preserving the membrane from chemical attacks by the solvents in the catalyst ink. However, it seems that the CL does not come into close contact with the membrane and therefore the electrode is prone to delamination. Regarding CCM, there are two ways of applying the catalyst ink to the membrane, namely the decal transferring process and the direct coating process. In the former, the CL is cast onto a PTFE blank... 

Membrane-based Hydrophilic Catalyst Layer. Wilson and Gottesfeld [8, 21-23] suggested an ionomer-bonded hydrophilic catalyst layer prepared with the decal transfer method. The so-called decal transfer process includes two key steps (1) coating catalyst ink onto a blank substrate (e.g., PTFE film) then (2) transferring the coat onto the membrane (as shown in Figure 19.6). A typical preparation procedure is as follows ... 

FIGURE 2.15 A schematic representation of the procedure for MEA fabrication using the decal transfer process [83]. (For color version of this figure, the reader is referred to the online version of this book.)... 

In most industrial processes, the electrodes are prepared from a so-called ink consisting of the supported catalyst powder, ionomer, and additives. Already here, the chosen carbonaceous support material will affect the ink properties, such as homogeneity and viscosity, and therefore necessitate adapted ink recipes for each support material. The ink is then either airbrushed, sieve-printed, inkjet-printed, or DECAL transferred onto the membrane or the GDL and - like the ink ingredients - also the chosen manufacturing process strongly affects the electrode properties. 

Typical processes for the electrode manufacture include airbrushing, sieveprinting, and a DECAL transfer step. In these processes, it is difficult if not impossible to control the integration of active sites, pores, and interconnected proton and electron pathways. That is why the systematic manufacture of (aligned)... 

Figure 19.6. Process flow diagram of thin film decal transfer technology...

Aside from the above process, a decal transfer method has also been developed to make a thin-film electrode [81-83]. The catalyst ink is first coated onto a decal substrate (such as PTFE film or Kapton film) by spraying or by using the doctor blade technique. The catalyst ink is then transferred to a Nafion membrane by a hot-pressing process to form a catalyzed membrane. This decal transfer method is presented schematically in Fig. 2.15 [83]. 

Decal Method In this technique, thin CLs are cast or spread onto a nonadhesive medium, and decal transferred onto an electrolyte by hot-press compression (similar to a clothes iron). This method is suitable for mass production of catalyst layers, with high tolerance and batch processing capability, although the physical bond between the electrode and the electrolyte must be carefully maintained. 

Figure 5 Kinetically controlled decal transfer printing, (a) Schematic drawing of the process used to transfer microfabricated structures from a donor substrate to a polydimethylsiloxane (PDMS) stamp, and then from the PDMS stamp to a receiver substrate, (b and c) scanning electron microscope (SEM) images oftwo-and three-dimensional structures fabricated by this process. Reproduced with permission from MeitI, M. A. Zhu, Z. T. Kumar, V. etal. Nat. Mater. 2006, 5,33-38. Copyright 2006, Nature Publishing Group.

Note that although the aqueous-based formulations are well suited to decoration of ceramic ware by brushing and direct screen printing applications (onto flat ware such as tiles or glass), the decoration of ware by decal transfers is more complex for these systems because they use water to release the transfer from the decal paper. It is reported that cross-linking aqueous polymer systems can be utilized to produce water-resistant films suitable for water-slide decal use, but no spedlic examples of any such formulations are recorded [26]. Alternatively, the aqueous gold formulations can be printed onto heat release transfer paper and used to decorate ware using an automated application process. 

As seen in Fig. 22, ME As based on such thin-film catalyst layers can be constructed using a decal process, in which the ink is cast onto Teflon blanks for transfer to the membrane by hot-pressing. A second approach is to cast the same type of ink (TBA+ form of the ionomer) directly onto the membrane [12]. The latter process has an advantage over the decal process in... 

Decals are also a means of transferring a design or printed message to a plastic part. With decals the decoration is placed on a decorative adhesive-backed film and then on a paper backing. The adhesive is such that it activates when in contact with water. To apply, the decal is moistened in water and the film is placed on the plastic surface. The process is not widely used because of the difficulty in accurately placing the decal in a specific location on the surface. 

A method known as the transfer decal process can be used to transfer the conductor layout from a film to a plastic body. The conductor side of the film is backfilled and then the film is peeled off the finished MID component. This process requires low adhesion between backing film and backfill material. A low-strength bond between conductor tracks and backing film is also essential. The conductor tracks can be surface-treated to ensure good adhesion to the backfill material [48]. 

Heat-release transfers offer an alternative process in which the gold ink is applied to a wax coated paper. The application of these decals to ware is an automated process where machinery melts the wax and transfers the decals to the ware to be decorated. Although this method is much faster, and requires no drying time, it requires significant investment in machinery and is suited to much higher-volume industrial applications, and most of the gold decal business remains as water-slide decals. 

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