Films biaxially oriented

There are other differences between cast, monoaxially oriented, and balanced biaxially oriented film. Typical figures illustrating these effects are given in Table 11.5. 

In this review the definition of orientation and orientation functions or orientation averages will be considered in detail. This will be followed by a comprehensive account of the information which can be obtained by three spectroscopic techniques, infra-red and Raman spectroscopy and broad line nuclear magnetic resonance. The use of polarized fluorescence will not be discussed here, but is the subject of a contemporary review article by the author and J. H. Nobbs 1. The present review will be completed by consideration of the information which has been obtained on the development of molecular orientation in polyethylene terephthalate and poly(tetramethylene terephthalate) where there are also clearly defined changes in the conformation of the molecule. In this paper, particular attention will be given to the characterization of biaxially oriented films. Previous reviews of this subject have been given by the author and his colleagues, but have been concerned with discussion of results for uniaxially oriented systems only2,3). 

For this case, which is the fairly common situation of a biaxially oriented film, it is therefore necessary to obtain a total of thirteen second and fourth order coefficients. Later, results for polyester films will be discussed, where seven of these thirteen coefficients have been determined experimentally. 

The determination of polarization direction is parallel or perpendicular to the draw direction. theoretical analysis are given in detail in a separate publication 6). 

Fig. 11. B20/a2 plotted against P2(0)overa together with the theoretical boundaries (A) for wholly gauche oriented material (B) for wholly trans oriented material. Draw ratios (a) 2 1 (b) 2.5 1 (c) 5 1 for one way drawn biaxially oriented film (d) 3.25 1 for uniaxal drawn rod. Reproduced from Polymer by permission of the publishers, Butterworth Co (Publishers) Ltd. (C)...

Biaxially oriented films, made by stretching in two mutually perpendicular directions, have reduced creep and stress relaxation compared to unoriented materials. Part ot the effect is due to the increased modulus, but for brittle polymers, the improved behavior can be due to reduced crazing. Biaxial orientation generally makes crazing much more difficult in all directions parallel to the plane of the film. 

PEN has excellent gas-barrier properties. The gas-permeation coefficients of unoriented cast film and biaxially oriented films for PEN and PET are given in Table 10.4. 

Uniaxially oriented films generally have high strength in only one direction, whereas biaxially oriented films are relatively strong in both machine direction (MD) and transverse direction (TD). Although intuitively one might expect biaxially oriented films to be preferred over uniaxially oriented films. 

Mechanical properties of polymers are improved by orientation processes [22, 24, 29]. Because of the biaxial orientation, films from blown film lines exhibit, e.g., a high puncture and tear propagation resistance. Blown film lines can be designed to produce flexible PE-LD or PE-HD films of 5-200 pm. 

Biaxially oriented films such as PET and PEN are birefringent. For LC displays which depend on light of known polarization this means that birefringent films, which would change the polarization state, are unlikely to be used as substrates. Films based on amorphous polymer are not birefringent and are more suitable for LC displays. Birefringence is not an issue with OLED, electrophoretic displays, or, indeed, some LC displays. 

Different methods are used. An online ordinary common blown or cast film line uses a machine direction orienter (MDO) on the front end of biaxially oriented film heated chamber extrusion line. If only the machine direction is to be stretched, a series of precision controlled heated rolls can be used. Film is fed through a series of rolls where it is sequentially heated, drawn around rolls that increase in rotational speed providing the stretching action, annealed around larger diameter roll(s), and cooled on a final roll(s). 

Figure 5.19 Example of upward extruded blown film process for biaxially orienting film...

The general purpose film grade is biaxially oriented , a property that gives it stability at temperatures up to 130 °C. They also offer a biaxially oriented film for high temperature applications (150 °C). According to NatureWorks, these resins offer excellent optical properties, good machinability and excellent twist and dead fold characteristics. These polymers are offered in common pellet form, which should allow for rapid adoption with conventional extruders. 

In 2004, Toray Industries, Inc. succeeded in developing the world s first plasticiser-free flexible PLA film using Toray s own nano-structure control technology for biaxially oriented films. This film, without losing the transparency and heat resistance features of PLA, has achieved superior flexibility levels, meaning it could be used as packaging films such as wrapping films. Toray are confident that the environment-friendly features of PLA film are expected to spur widespread demand in the future. 

Samples. Polyethylene terephthalate (PET) samples are industrial (Mylar) biaxially oriented films (10 pm thick). Polymethyl-methacrylate (PMMA) has been spin coated on microscope glasses from a PMMA (1) / CHjClj (9) solution, giving thin layers of a few hundred A thickness. 

PBZT and PBO are ordered polymers which form long rigid-rod molecules which give rise to a microfibrillar network structure in biaxially oriented films (Figure 1). Such biaxial films have been used in combination with low dielectric constant resins, such as cyanate ester resins, to make circuit substrates for use in MLBs... 

As a result of this the manufacturers of polymers have found it necessary to exercise leadership in pioneering the methods by which their polymers are formed—sometimes to the extent that the manufacturer has himself often sold the polymer in the fabricated form. Hercules, for example, pioneered in the manufacture and sale of polypropylene resin. We soon realized, however, that the conversion of this resin to fiber and to film and to foam, would have to be done by us because of the complex technologies and large investments involved. Consequently, the resin manufacturer now finds himself selling polypropylene fiber, biaxially-oriented film, and foam—successfully too if I may be allowed to add. 

The effect of orientation on amorphous barrier resins SELAR PA 3426 and XHTA-50A are shown in Table III. The measured oxygen permeability of 1.4 cc-mil/100 in 24 hr. atm for unoriented extrusion cast SELAR PA 3426 film is reduced by 19% upon uniaxial orientation, while the permeability of biaxially oriented films are 28% lower than that of extrusion cast film. Similarly, the decrease in oxygen permeability with 2X and 2.5X uniaxial orientation in XHTA-50A are 5% and 9% respectively, from the measured value of 3.1 cc-mil/100 in 24 hr. atm for unoriented film. The corresponding reduction in permeability with 2X x 2X biaxial orientation is 12%. 

Monoaxially and biaxially oriented films of fluoropolymer are made by melt extrusion of the resin into flat webs or tubes. The main function of orientation is to enhance the mechanical properties of the film such as tensile break strength and tear resistance. The decision to orient is usually made according to the requirements of the end use for mechanical properties. All process surfaces that contact molten fluoropolymers must be corrosion resistant because of the formation of corrosive compounds such as HF and HCl from the high-temperature degradation of these plastics. 

In another example, unoriented PVDF films were stretched at 150°C in the longitudinal direction at a stretch ratio of 3.5 to 1. A sample of the longitudinally oriented film was stretched in the transverse direction at 60°C at a stretch ratio of 3.4 to 1, thus producing a biaxially oriented film. Dielectric constant and loss factor values were measured for these films (Table 6.10). 

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