Other Inorganic Barrier Coatings

There are three major processes for applying the silicon oxide coating evaporation, sputtering, and chemical plasma deposition. 

Aluminum oxides can be used in place of silicon oxides for coating films, and combinations of SiO and MgO have also been used, resulting in transparent films with enhanced barrier properties. Evaporation using electron beams is used to deposit the aluminum oxide (or other metal oxide) on the base resin. There has also been investigation of coatings that are combinations of SiO and MgO. 

Amorphous carbon has also been used as a barrier coating. One of the major players is Sidel, with its Actis coating, which permits PET to be used for beer bottles, achieving up to a six month shelf life [2]. Mitsubishi also has a system for depositing an amorphous carbon coating, which they term DEC, diamond-like carbon [3]. 

In this process, PET bottles are placed in a vacuum chamber, acetylene gas introduced into the bottle, and a plasma generated, forming a 10 to 30 nm coating on the inner surface of the bottle. Oxygen barrier is reported to be improved 15 times or more, carbon dioxide barrier 10 times or more, and water vapor barrier 6 times or more. 

Clay nanocomposites are also being developed as barrier coatings for film and for containers. The nanocomposite is deposited on the film from a solution of PVOH/ EVOH copolymer in a mix of water and isopropyl alcohol which has been used in a supersonic dispersion system to nano-disperse 7 nm diameter silica and titanium dioxide particles. The ratio of polymer to silica depends on the barrier properties required. Typical microgravure equipment can be used to coat the solution onto a plastic substrate. The result reportedly is a transparent barrier coating which is superior to silica- and alumina-coated films, and is comparable to aluminum-coated materials. Oxygen permeability at a coating thickness of 2 pm is less than 1 cc/m d atm, and moisture permeation less than f g/m d. Costs are reported to be competitive with ceramic coatings [4]. 

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In order to reduce the intrinsic porosity and to increase the barrier effect of anticorrosion CP-based coatings, composite systems have been considered where one component is a CP and other component can be organic or inorganic. In literature, several recent papers have been published on this topic. Two classes of composites based on CPs could be individuated (Table 10.4). In the first class, the matrix is a CP, usually PANI and its... 

As explained in Chap. 14, anodizing is a widely use technique to produce a protective inorganic coating of some engineering materials such as aluminum, magnesium, titanium and a few other metals and alloys by the application of an anodic potential that would be normally quite corrosive if it was not for the barrier created by the process itself. Of all metals that are routinely anodized, aluminum alloys are... 

PVD processes are traditionally used for the deposition of various coatings on tools and components and other metallic or ceramic substrates, for example, to improve surface hardness, wear resistance, and corrosion resistance. However, more and more plastic products are used today in fields where metals were previously predominant. In these cases, the end product should meet functional requirements (durability, scratch, corrosion, and chemical resistance) and decorative appearance. Another important application includes metallized and transparent inorganic gas-diffusion barrier layers on packaging films. 

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