Coatings on flexible substrates

Coatings on flexible substrates are considerably thinner, typically in the range 1 to 30 g/cm2, but the production rates are high (100 to 300 m/min), therefore, lower-energy electrons and moderate- to high-power beams are required.108... 

Plasma treatment of PDMS followed by adsorption of self-assembled silane monolayers has enabled us to controllably modify the surface energy of elastomer surfaces as described in the section on the Johnson, Kendall, and Roberts approach to deriving the surface free energy of solids. A similar treatment of silicon substrates has produced a useful, low—hysteresis model substrate for contact angle study. There are three types of PDMS contact angle substrates usually studied fluids baked or otherwise chemisorbed on solids such as glass or metals cross-linked coatings on flexible substrates, such as paper or plastic film PDMS elastomer surfaces. 

The encapsulation process for ChLC is mainly attributed to its transport and optical properties [15]. Firstly, since viscosity of pure ChLC is close to that of water, its fluidity prevents ChLC from being coated on flexible substrates. Secondly, when a cholesteric liquid crystal is pressed, the flow generated inside makes the displayed image erase. Therefore, droplet dispersions by encapsulation act as a protector for its bi-stability and optical properties. The additional advantage is that encapsulated cholesteric liquid crystals are self-sealing the materials confined to the droplets cannot flow through an interface of the droplets. 

Electrodeposition has been attempted also on flexible substrates within the scope of fabricating flexible solar cells. Huang et al. [177] investigated the electrodeposition of CIS on Au-coated plastic substrate from aqueous acidic (pH 1.65) solutions of millimolar CuCh, InCb, Se02, containing triethanolamine and sodium citrate. Stoichiometric, semiconductive CIS films (Eg = 1.18 eV) were obtained after annealing at 150 °C in nitrogen. 

Extrusion coating has been developed to form thin polymer layers on flexible substrates like paper, paper board and metal foils in a high speed process (see Fig. 10) [27, 33, 34]. In combination with paper and paper board, the polymer protects the substrate from moisture, oil and fat. The polymer provides the welding properties to transform, e.g., the paper board/PE substrate into a paper cup, a liquid packaging board or a box for frozen food. 

Control of the EB cured film properties through formulation is the key to meeting specific end use properties. A wide range of hardness and flexibility can be produced by adjustment of crosslink density and glass transition temperature. Studies on the effects of formulation variables on the tensile elongation properties of free films have proven especially valuable in development of coatings for flexible substrates. 

Adhesion tests may be divided into the methods by which stress is applied to the lilm/coating. Adhesion test methods include tensile tests, peel tests, shear tests, deformation tests, energy deposition tests, fatigue (thermal, mechanical) tests, and many others. Some of these tests are depicted in Figure 12.3. Adhesion testing of thin films on flexible substrates such as webs is a particularly difficult problem.f ... 

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