Chapter 37
Oxygen Gas Barrier PET Films Formed by Deposition of Plasma-Polymerized SiOx Films
Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 11, 2015 | http://pubs.acs.org Publication Date: May 4, 2000 | doi: 10.1021/bk-2000-0729.ch037
N. Inagaki Laboratory of Polymer Chemistry, Faculty of Engineering, Shizuoka University, 3-5-1 Johoku, Hamamatsu 432-8561, Japan
In order to prepare SiOx-deposited PET films with a high oxygen gas barrier capability, SiOx depositions from the plasma polymerization of silane compounds have been investigated from viewpoint of the chemical composition of the deposited SiOx films and oxygen permeation rate through the SiOx-deposited PET films. Tetramethoxysilane (TMOS) was suitable as a starting material for the SiOx deposition from the plasma polymerization. Oxidation and etching processes by selfbias effects were effective in the SiOx deposition. The SiOx film deposited on PET film surfaces from the TMOS/O2 mixture (60 mol% O2) was mainly composed of Si-O-Si networks with a carbonized carbon component as a minor product. The SiOx-deposited PET film showed good oxygen gas barrier properties. The oxygen permeation rate was 0.10 cm3/m2day-atm, which corresponded to an oxygen permeability coefficient of 1.4 x 10-17 cm3-cm/cm2-sec-cmHg for the SiOx film itself. This permeability coefficient is three orders lower than that of conventional gas barrier polymeric films such as Eval and Saran.
Silicon oxide film (SiOx) is an interesting material in the field of the food and pharmaceutical technologies as well as the microelectronics technology. SiOx film possesses a high gas barrier property besides high thermal stability and high electrical insulation. Therefore, SiOx-coated polyester (PET) film is a possible material used for packing to protect foods or medicines from the deterioration by oxidation. Usually, SiOx film is synthesized by the sol-gel method using alcohoxysilanes such as tetraethoxysilane (TEOS) or by the plasma chemical vapor deposition (plasma CVD) methods using a mixture of TEOS and oxygen (i). In these processes, TEOS is hydrolyzed and polycondensed into Si-O-Si networks. Building-up the complete SiO-Si networks and eliminating carbonaceous components from the deposited SiOx film requires a high temperature of more than 500*€ (2). However, this process is difficult to apply directly the preparation of the SiOx-deposited PET films because of low thermal-resistance. The SiOx film deposition should proceed at lower temperatures than the glass transition temperature (about 70°C) of the PET film.
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© 2000 American Chemical Society In Silicones and Silicone-Modified Materials; Clarson, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.
Downloaded by KTH ROYAL INST OF TECHNOLOGY on August 11, 2015 | http://pubs.acs.org Publication Date: May 4, 2000 | doi: 10.1021/bk-2000-0729.ch037
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A possible process for the SiOx film deposition at low temperatures below 70°C may be a special plasma C V D method which involves some elimination of carbonaceous compounds. In the plasma CVD, we believe that SiOx films are formed in two reactions: (1) the bond scission of Si-O-C bond in TEOS to form Si» or SK> radicals, and (2) the recombination between two radicals to form Si-O-Si linkage. The repetitious combination of the two reactions leads to the Si-O-Si network, and as a result, a SiOx film is deposited. On the other hand, fragments eliminated from TEOS, ethyl or ethoxy radicals, also are recombined to form carbonaceous compounds and incorporated into the SiOx film. In the conventional plasma C V D process, the carbonaceous compounds in the deposited SiOx film are eliminated by the pyrolysis of the SiOx film at high temperature (500
