Film/coating properties pinholes

Some other PFs end capped with cross-linkable groups, such as benzocyclobutene, have been patented by Dow Chemicals [275-277]. For example, the thermal curing of spin-coated polymer 232 gave an insoluble pinhole-free film without alteration of the fluorescent properties (Chart 2.57). 

The significance of pinholes in foil has a relatively small influence on the overall barrier properties, provided the pinholes are filled in on either or both sides by a plastic film or coating. Pinholes normally occur randomly and are usually less than 25 4 m (0.001 inches) in diameter. Due to the random nature, a proportion fall in the seal area and non-seal area of most packs. Where the pinhole falls into the latter, the permeability relates to the area of the pinholes and the permeability of the film(s) involved. 

Parylene is widely used as a protective coating in the field of electronics, aerospace and medical applications. Parylene is formed on surfaces from the gas phase, in contrast to most other coating techniques that use Uquid precursor materials. The resulting film is thin and conformal, has no pinholes at sufficient thickness, and is chemically resistant. The coatings impart several properties concomitantly, including electrical insulation, moisture and chemical isolation, mechanical protection, enhanced lubricity. The poor adhesion of the surface rejects dust and soil. 

The ease of preparation and the unique properties of the polymers produced by plasma polymerization have lead to applications for pinhole-free films in protective coatings, insulating layers, and membranes for reverse osmosis. 

They also formed the condensed polynuclear aromatic (COPNA) resin film on a porous a-alumina support tube. Next, a pinhole-free CMSM was produced by carbonization at 400-1,000°C [29], The mesopores of the COPNA-based caibon membranes did not penetrate through the total thickness of each membrane and served as channels which increased permeances by linking the micropores. CMSMs produced using COPNA and BPDA-pp ODA polyimdes showed similar permeation properties even though they had different pore stractures. This suggests that the micropores are responsible for the permselectivities of the carbonized membrane. Besides that, Fuertes [30] used phenohc resin in conjunction with the dip coating technique to prepare adsorption-selective carbon membrane supported on ceramic tubular membranes. 

The Parylene conformal coatings are ultrathin, pinhole-free polymer coatings that provide a number of high-value surface treatment properties, such as, excellent moisture, chemical and dielectric barrier properties, thermal and UV stability, and dry-film lubricity. These properties make Parylene coatings the ideal choice for a number of industrial applications throughout the medical device, electronics, automotive, military, and aerospace industries. Some examples are listed [155]. 

Polymers can be evaporated, deposited as a thin film, and cured in a vacuum system to provide a basecoat. For example, acrylate coatings can be deposited and cured with an e-beam. The deposited liquid flows over the surface and covers surface flaws, reducing pinhole formation. This technique can be used in vacuum web coating and has been found to improve the barrier properties of transparent barrier coatings. 

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