VACUUM METALLISATION

OPP producers have expanded the core, creating a foam stmcture with lower density, greater opacity, and a stiffer, more paper-Hke feel. Vacuum metallisation increases opacity and water-vapor barrier properties. 

Classified nylon is now available which can be vacuum metallised and chromium plated. It is used in electric drill housing telephone relay bobbins, car door handles, etc. 

Vacuum Metallising Cycolac, Technical Report P135, Borg-Wamer Corp., Chicago, Ik., 1980. 

Adhesion to the film can be enhanced by surface treatment. The conventional method is corona discharge but more recently atmospheric pressure oxygen plasma treatments have been developed. The film can also be vacuum metallised to improve barrier performance, coated with copper for surface conductivity or with more advanced coatings such as sapphire. Mineral fillers can be used to provide higher modulus and to the control coefficient of thermal expansion in relation to particular coatings or specific applications. 

Table 5.50 lists the main features of Raman microspectroscopy. Virtually any object which can be observed under a microscope can be analysed with Raman microscopy. Here, the usual constraints inherent in electron beam methods (vacuum, metallisation, etc.) are totally absent. Although micro-Raman spectrometers mainly use visible excitation, the confocal configuration almost eliminates fluorescence which falls outside of the focal volume. The focus area for visible lasers is <1 /xm, whereas the focus diameter for NIR lasers is 20 fim. 

In vacuum metallising, a metal is heated in a vacuum chamber to its vaporisation point, which is lower than the melt temperature of plastics. The metal vapour deposits on the cooler plastic surface. In electroplating, an electric current is used to deposit metal from a metal salt solution onto a plastic rendered conductive by electroless plating. Arc flame, arc spraying, and sputtering are other techniques used. Metallising requires very clean surfaces, free from mould release agents. Primers or pre-cleaners can be used to improve the adhesion of the metal to the polymer surface. 

The only other major group of thermosets are the phenol formaldehyde and urea formaldehyde plastics. These are often used for closures in the cosmetic industry and are either coated to colour co-ordinate the component or vacuum metallised. 

Acrylic lacquers are used both as basecoats and topcoats in vacuum metallising applications on a number of plastic substrates, including polyester, nylon, acrylic, polyethylene, polystyrene and PVC. The function of the basecoat is to provide a good key between the substrate and the vaporised aluminium metal and to fill the imperfections in the substrate, thus enhancing the brightness and reflectivity of the deposited metal. The basecoat must also have extremely low volatility, since volatile by-products released under vacuum would lead to a poor quality deposition. The fast lacquer drying properties of acrylics and the non volatile inert nature of the polymer film make them an ideal choice for this application. 

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. 

Another way of surface improvement is metallising. Very thin metal layers (up to a few pm), are deposited by evaporating the metal under vacuum. This method can be applied to all types of plastics. Metallised films find their application in electrotechnics and as reflectors for radiant heat. In an electric oven aluminium is evaporated, while the vapour is precipitated on the surface to be treated in most cases an extra protective transparent layer is added. 

J. L. Vossen, Bibliography on Metallisation Materials and Techniques for Silicon Devices, Vols. 6 (1980), 7 (1981), and 8 (1982), American Vacuum Society, New York. 

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. 

As catalysts are generally insulating, it is necessary to metallise the surface to be examined and ensure that it is earthed in order to enable the flow of charge from the electron beam. A metallization layer (generally made of carbon) is deposited via thermal evaporation under vacuum (carbon has the advantage of not being particularly absorbent vis-a-vis the incident electrons and vis-ii-vis the characteristic X-rays). The electrical contact with the sample holder is created using a silver or carbon lacquer. 

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. 

Plastics can have a layer of metallic aluminium deposited on the surface by vacuum. Although aluminium is basically a bright silver, it may be lacquer tinted to give a wide range of metallic colours. Polyester, polystyrene, urea and phenol formaldehyde, and polypropylene are readily metallised. Other plastics need a pretreatment. 

Ths metallisation process took place in a OHV chamber connected to an x-ray photoalactron spectrometer separated by a gate valve, specimens were transported between the spectrometer and deposition chambers under UKV with the use of vacuum transporters and wobble sticks, cr was deposited onto the polymer surfaces by Ar ion beam sputtering with a saddle field ion source (Model Bll, Ion Tech Ltd.) operating at 4 kv. The polycrystalline Cr target (99.8% pure, cerac,... 

In order to make a metallised film capacitor the polymer has a layer of either aluminium or zinc vacuum evaporated on to its surface. Once the capacitor has been wound a gradually increasing potential known... 

E.g. Metallising, this is the deposition of an aluminium layer, h the order of 1000 Angstroms onto a basecoat The most common method is vacuum deposition where alwnmium is evaporated in a high vacuum envirorunent. ... 

---