Priming surfaces

Fig. 10. Plate-—coil heat exchangers. Plate—coil is a very efficient and versatile prime surface-type heat exchanger.

Other aspects of interfacial science and chemistry are examined by Owen and Wool. The former chapter deals with a widely used chemistry to join disparate surfaces, that of silane coupling agents. The latter chapter describes the phenomenon of diffusion at interfaces, which, when it occurs, can yield strong and durable adhesive bonds. Brown s chapter describes the micromechanics at the interface when certain types of diffusive adhesive bonds are broken. The section on surfaces ends with Dillingham s discussion of what can be done to prime surfaces for adhesive bonding. 

Its best use is for bridges, gantries, conveyor-belt steelwork, etc., where the relatively drab, matte appearance can be tolerated. The Department of Transport uses this material on inland motorway bridges, and has found that, if applied to a correctly prepared and primed surface, it can be substantially maintenance-free for 20 years. 

A unique two-coat, topcoat system is used in the automobile industry. A basccoat is applied to a primed surface to provide opacity, color, and a metallic appearance, while the clearcoat provides gloss mid a miiioilike finish (referred to as distinctness of image). 

A minimum penetration of water to the interface. Silane coupling agents, themselves, may contribute hydrophilic properties to the interface. This is especially true when amino-functional silanes are used as primers for reactive polymers such as epoxies and urethanes. The primer may supply much more amine functionality than can possibly react with the resin at the interface. Excess unreacted amine at the interface is hydrophilic and is responsible for the poor water-resistance of such bonds. The amount of excess amine at the interface may be minimized by using very dilute solutions of silane in the primer, or by washing the primed surface with water or organic solvent to remove all but a very thin layer of chemically adsorbed silane. 

Immerse for 5-10 min at 90°C in potassium permanganate (saturated solution), acidified with sulfuric acid (96%). Rinse in water and distilled water. Dry in warm air. 4. Prime surface with a lacquer based on urea formaldehyde resin diluted with carbon tetrachloride. Coatings (dried) offer excellent bonding surfaces without further treatment... 

The undercoats are pigmented paints that are applied to primed surfaces prior to the application of finished coats. The undercoats are high pigment paints with a matte finish and a color to complement that of the ultimate finishing coats. 

Micrographs of the failure surfaces show good adhesion between the adhesive and the primed surface. Fig. 15.2 shows the failure surfaces of Al adherend bonded with the epoxy adhesive. The failure mode is cohesive in the epoxy adhesive. The improved interlocking of the adhesive in the primed surface topography is presented in Fig. 15.3. 

SURFACE FIEATING - The exterior surface of a heating unit. Extended heating surface (or extended surface), consisting of fins, pins, or ribs which receive heat by conduction from the prime surface. Prime surface heating surface having the heating medium on one side and air (or extended surface) on the other. 

Choice of an appropiate surface treatment and a suitable primer are important because adhesion to the substrates presents difficulties [11.37]. Primers based on modified alkyd resins or two-pack epoxy-resins for derusted ferrous metals mainly contain zinc phosphate and zinc OKide as corrosion protection pigments. Nonferrous metals are first washed with an ammoniacal wetting agent before applying the primer that contains a binder based on synthetic resins (e.g., PVC copolymers, chlorinated rubber) which ensure good adhesion to the substrate. The same primer must be used on zinc or galvanized surfaces because the use of alkyd resins causes embrittlement [11.38] The primed surfaces are largely topcoated with alkyd resin systems. 

Prime surface with lacquer based on urea-formaldehyde resin diluted with carbon tetrachloride... 

Extended surfaces are normally produced with fins either longitudinal or transverse to the tube axis. Other forms are also available, but not widely used. Fins may be attached to the prime surface by some mechanical means hence there is a bond resistance to heat transfer which increases with the temperature of the application. Fins may also be manufactured by extrusion from the prime tube or by welding fins to a tube both of these techniques eliminate any bond resistance. 

In the bonding of rubbers it is assumed that the plastics component is an item which has been preformed and it is this which will be treated with a bonding agent. In most cases the rubber will be moulded onto the primed surface, by techniques including the following ... 

A general guide to reduce the effects of water adsorption is to dry the plastic s surface, prime with the bonding agent, dry the primed surface and give the component a prebake (the coated dried surface is heated, prior to the moulding process). Pre-bakes can... 

Aquaforte 108-W should be applied to the substrate and dried. The extradite, lamination or printing inks will then rigorously bond to the primed surface. 

Polaqua W7 should be applied to the substrate and dried. The extrudata, lamination or printing inks will then rigorously bond to the primed surface. The substrate may be primed and rewound for subsequent use at a later date up to 90 days with no blocking or reduction in bond strengths. 

Polaqua 103-L is applied to the film surface and dried. For best results, especially with certain grades of polypropylene, it is recommended to have the accepting surface corona treated. The extrudate, lamination or printing inks will then rigorously bond to the primed surface by heat and pressure application. 

The primed surfaces are then allowed to dry. This can be accomplished by forced drying (at elevated temperatures in an air-circulating oven) or, traditionally, over night at ambient temperature. Depending on the primer and the application, the primed surfaces can be stored in the dried state until required or they can be oven-cured prior to later use. 

Primer. This will involve a separate stage in manufacture. Some adhesives will only function on correctly primed surfaces. This is an issue quite separate from the question of whether a siloxane primer is desirable for special environmental conditions (see Chapter 6). 

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