Metallised coatings

Flame spray metallising is widely used for the protection of metal against corrosion, especially for in situ protection of stmctural members. The principal metal used for spraying of plastics is sine. Aluminum and copper are also used. If the distance from the part is too great, the zinc solidifies before it touches the part and adhesion is extremely poor. If the molten zinc oxidizes, conductivity and adhesion are poor. If the distance is too short, the zinc is too hot and the plastic warps or degrades. These coatings are not as dense as electrically deposited coatings because of numerous pores, oxide inclusions, and discontinuities where particles have incompletely coalesced. 

Interference patterns with the reflective and refractive light occurs that varies with the viewing angle. Thin metallic flakes of, for example, aluminium, copper, bronze, coated with a dye are used extensively in automobile wheel hub-caps, and "metallised" car-body paint finishes. 

A final method is metallisation11 of fibres, which is most related to the technology described in this chapter. In this method, metal salts are taken up by the fibre and reduced to their metallic conductive form. Metallisation can be achieved in different ways. A first way is by a vacuum metal spray. However, this results in very poor defined metallisation. In addition, galvanic coating is used in the production of conductive fibres, but this type of coating requires a fibre that is already conductive. 

Galvanisation of the metallised fibre will improve its properties as electrical conductor because of the formation of a continuous metallic coating at the surface of the fibre. In this respect, the seed layer formed during metallisation is crucial for a good adhesion between the metal layer and the PAN-fibre structure. 

All the results were confirmed by investigations with both back- and front-side illumination [37]. In this study, which also describes theoretical aspects, a final resolution of 17 pm for an epi-structure was achieved, which consisted of a thin layer (3 pm, specific resistance of lOQcm) and a thick silicon substrate (0.38 pm, with low specific resistance of 0.005-0.02 Q cm). Instead of using a pattern grid on the front-side to study the smallest possible resolution, in this work the sensor chip was coated half with a metal layer. This forms on the covered side a metal-insulator-semiconductor (MIS) structure. The light pointer was moved from the metallised area to the uncovered area and the resolution was determined at the borderline by measuring the photocurrent that depends on the diffusion length of the carriers. Since, for the assumption that the diffusion length is the main decisive and critical parameter for the amount of carriers which could reach the metal-covered part of the semiconductor substrate from a specific distance, the calculation of the minimal resolution was experimentally observed. 

Metallising Applying a thin coating of metal to a non-metallic surface. May be done by chemical deposition or by exposing the surface to vaporised metal in a vacuum chamber. 

Metallised PP/PP laminate (outer PP film reverse-printed with nylon-based resin ink) bag PP film (fuUy printed on outer surface) heat-sealed single packs packed in PP film heat-sealed multipack (partially printed on outer surface) Cartonboard boxes in PP film overwrap (coated on both surfaces with VdC copolymer)... 

Under the conditions studied, the relative effectiveness of primary packaging materials in terms of reducing transfer of substances from secondary (2°) packaging to MPPO was PET >nylon> PVdC-coated PP > metallised PP/PP laminate > PP > paper. 

It is necessary to distinguish between the preparation time (coating, polishing, metallisation, etc.-taking about one hour per sample) and the analysis time in the strict sense of the term, which varies depending on the type of analysis required. A quantitative analysis takes between 1 and 2 hours for 5 profiles. 

Figure 18.12 a) Simplified model of lift-off structured contacts where the metal layer is coated at high conformity, h) Same model for a metallisation deposited hy low conformity. 

These may be used for bulk excipients where there is no risk to or from the environment, e.g. chalk. They comprise two to six plies of sack Kraft types of paper, with possibly LDPE coated or metallised paper or one ply of LDPE in the case of composite sacks. The sacks may or may not have a gusset. They will all be either stitched or glued at the base and usually stitched to close the open mouth. 

The use of other plastics tends to be related to specialised needs and whether their advantages justify the additional cost, e.g. Aclar (trade name) may cost twenty times more than PET but is the nearest approach to an inert plastic and is approximately ten times less permeable than Saran (PVdC—polyvinylidene chloride) which is widely used as a film coating. However foil, even when thin (0.006 mm and above) remains the best barrier material, with newer techniques of film metallisation, especially where two contact layers are used, coming a close second best. 

The above heading has been selected to include all variants which may be now used for both flexible and rigid applications. Whereas previously these may have been introduced under flexibles , film, foils and laminates , etc., the use of new technology such as coextrusions, metallisation and different coating techniques has produced some confusion as to what terminology should be employed, so the word multi-layer may be more appropriate. 

Unless PVdC coated or metallised, OPP is a poor gas barrier and needs pretreatment prior to printing. 

It is heat seal resistant unless produced as a coextrusion or coated. A good barrier to most gases and volatiles, but only fair to moisture. It is easily metallised. Found as PETP and PETG (Kodak), Pet G contains an additional glycol molecule. 

Any laminate may consist of a number of plies selected from paper, cellulose, films, foil, coatings, tie layers, metallisation, etc. From previous pages the permutation possibilities are enormous. However this choice is restricted by ... 

These are produced by several conversion processes (evaporation, sputtering, chemical plasma deposition). Evaporation is the same method as that used to create metallisation using aluminium. A material is heated in a crucible by either a resistive heat or an electron beam gun (hence the name electron beam deposition), whereby the material evaporates and subsequently condenses on a chilled film in a vacuum chamber. In the case of Sit), coatings, the aluminium used in metallisation is replaced by SiO/Si02. 

Vacuumised metal coatings are gradually improving. Tests indicate that these substantially increase the protection offered by plastic materials but do not equate with a ply of foil. Two plastic plies, each with a vacuumised foil, when laminated in direct contact with one another, can give excellent barrier properties. The barrier properties achieved by metallisation may reduce somewhat once the material becomes creased. Protection from some of these creasing effects can be improved by the incorporation of a more flexible ply (e.g. LDPE), i.e. PET metallised/LDPE. PET is very resistant to tear, hence needs a tear initiation feature. It also confers child-resistance. 

Improving Barrier Properties by coating, coextrusion, lamination, metallisation and overwrapping... 

The carrier may be glassine, cellulose film, and polyester film. The choice of carrier relates to speed and transfer temperature. Polyester (i.e. Melinex) is the most common base. It is suitable for flat, cylindrical or radiused surfaces. The process is used for online printing. Metallic foil consists of a carrier, release coating, lacquer metallised layer and a hot melt type adhesive specially formulated for the substrate. 

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