PEN films

PEN film for audio- and videotape and various electronic appHcations and blow molded PEN containers for hot-fill appHcations are already being marketed in Japan. NDA is unlikely to ever become as inexpensive as terephthaUc acid but novel NDA-based polyesters will become available if a market need exists. One example could be the experimental polyester PBN (Celanese Corp.) this is the NDA analogue of PBT, poly(l,4-butylene naphthalene-2,6-dicarboxylate) [28779-82-0]. It has a high rate of crystallization, faster even than that of PBT, and its combination of physical properties is weU-suited for injection molding. 

In the early 1990s interest developed in the packaging material polyethylene naphthalate (PEN), a close cousin of PET. PEN has thermal stability 20°C higher than PET. Kodak had samples of the material sifting in its labs from the makers Teijin in Japan, as early as the beginning of the 1970s. Teijin is still the premier producer of PEN film and plastic today, and is involved with DuPont on the film manufacturing side. 

Eldib Research Report, Year 2000 Market Survey on PEN Film in USA, http // www.eldib.com, 2000. 

Major PEN film applications include substrates for Advanced Photo System (APS) [2] film, where PEN s higher modulus permits the thinner, curl-free films required. Capacitors capable of higher temperature performance in industrial motor windings also make use of PEN s properties. 

CONTINUOUS PROCESS FOR THE MANUFACTURE OF BI AXIALLY ORIENTED PEN FILM... 

The amorphous PEN resin pellets are first dried at 180 °C and then extruded at 290-300 °C through a die, formed into a sheet, which is then followed by a two-step orientation (forward draw and sideway draw process) just above the glass transition temperature (Tg) (>120°C). After the orientation process, the PEN film is conveyed between rollers at 210-220 °C to induce crystallization. At the end of the orientation and crystallization process, the film is cut and rolled into widths and lengths to suit individual customers [14-16], Two of the process used to produce such films are shown in Figure 10.3. 

Figure 10.3 Manufacturing processes used to produce PEN films (a) simultaneous (b) sequential (MD, machine direction TD, transverse direction)...

PEN has lower gas permeation coefficients than PET for carbon dioxide, oxygen and moisture for both film types. Although the gas-barrier properties of PEN are similar to those of poly(vinyl dichloride), it is not affected by moisture in the environment. Both oriented and unoriented PEN films restrict gas diffusion more... 

In addition, PEN has better resistance to moisture absorption than PET and polyurethane [44], All of these properties endow PEN film with better electrical resistant properties than any other polymer. 

PEN films have strong electrical luminescence (EL) properties (Table 10.6). Under DC stress, the emission threshold for PEN is 1.5MVcm 1 while for PET it is 4 MV cm-1. 

Compared with PET, PEN has five times more radiation resistance in air, four times more in O2 and ten times more resistance in vacuum under continuous-use temperature [10]. Cakmak and co-workers calculated the refractive index of PEN this parameter is highest (nc = 1.908) along the chain axis and lowest (nn = 1.36) normal to the naphthalene ring. Biaxially oriented PEN film has a... 

PEN films provide specifications that meet the requirements. PEN shows high mechanical properties, low fogging during manufacture and storage, and excellent thermal dimensional stability, and can be made photo-reactive with the gelatin being reactive. Consequently, it is a good support material for advanced photosystems [55, 56],... 

The use of specialty substrates for labels have been driven by the market looking for materials with greater dimensional stability at higher temperature, improved mechanical performance under harsh environments, and resistance to scratching and tearing. Up until now, PET-based labels have been used where conditions are moderate, while polyimide-based labels have been employed in the most extreme environments. PEN films offer a unique performance advantage over PET and a considerable cost saving when compared to polyimide films. 

PET and PEN films have an inherent advantage over the amorphous polymers films being both semi-crystalline and biaxially oriented and typically absorbing approximately 1400 ppm moisture at equilibrium (the exact figure depending on temperature and relative humidity). Polyethersulfone and polyimide films are particularly problematic and will absorb over 1% moisture at equilibrium. 

The main properties of heat-stabilized PET and PEN relevant to flexible electronics are summarized in Fig. 7.9. Unstabilized PET and PEN films have the same set of... 

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