Bonding primer

There are specialist primers on the market for bonding polyurethane to metals. The three most popular brands are  

The prepared metal surface is coated with one or two coats of the primer, depending on the grade and the chemical and water resistance required. The coats must be applied at the recommended thickness. There is normally a minimum and maximum thickness. The aim is to fully wet the metal surface but not have too thick a layer. All the solvents in the primer must be evaporated before use. If the coated metal part is not used immediately, it must be carefully covered in polythene film to prevent surface contamination. 

The primer can be applied by brush, roller and doctor blade, or spraying. To lower the viscosity for spraying, the recommended solvent must be used. The most important point when applying the primer by spray is to ensure that the spray is still solvent-wet when it reaches the part. Dry material can cause poor bond strength. 

Once a part has been coated with a primer, it must be handled only with clean cotton gloves, preferably in a noncritical area. Parts that have had a long period between coating and molding may have to be freshened with a thin coat of primer. 

Certain primers require a prebake prior to use. This can at times be achieved while the reinforcing is being heated in the mold. 

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The usual approach to good bonding practice is to prepare the aluminum surface as thoroughly as possible, then wet it with the adhesive as soon afterward as practical. In any event, aluminum parts should ordinarily be bonded within 48 h after surface preparation. However, in certain applications this may not be practical, and primers are used to protect the surface between the time of treatment and the time of bonding. Primers are also applied as a low-viscosity solution which wets a metal surface more effectively than more viscous, higher-solids-content adhesives. Corrosion-resistant epoxy primers are often used to protect the etched surface during assembly operations. Primers for epoxy adhesive systems are described in Chap. 10. 

Paints Stains Varnishes Cleaners Conditioners Removing Agents Bonding Primers Floor Coatings... 

This will aid die stripping action of the proposed stripping solvent, benzyl alcohol. VOC have already been reduced in several components bonding primer (from 1030 to 850 gd), undereoats (from 670 to 350), top coats (from 700-900 to 250-800), clear coats (from 700-800 to 250-520), surface eleaners (from 850 to 250) as well as other materials. ... 

The phosphate treatment must be carefully controlled to ensure the quality and uniformity of the coating. The bonding primer must be applied within 24 hours of the phosphating process. 

Application of the primer coat to freshly prepared metal must be as quick as possible to prevent atmospheric agents causing corrosion. Oxide films (corrosion) are not usually securely adhered to the surface of the parent metal and thus can be easily pulled away. If the bonding primer has adhered to the corrosion layer it too will be pulled away from the desired contact between the primer and metal. This corrosion may not be visible to the naked eye, but can result in nnderbond corrosion continuing after vulcanisation. Obviously ambient conditions in the metal preparation area dictate the timing and speed of primer application. 

In the case of metal substrates primers are usually applied to protect the surface from contamination and hydrolysis as well as to enhance the durability of the bond. Primers are usually spray applied. Depending on the specific primer the thickness can vary from 0.1 to 2 mils. Prior to application of the adhesive, the primer is air dried or heat dried to remove solvents and in some cases heat cured. 

When painting over an oil-based stain, a bonding primer will keep your paint from rolling off like water from a duck s back. Use an oil primer for unfinished or weathered wood, distressed paint, varnish, or woods like redwood that bleed tannins and so require an oil-based primer to lock the juices inside. Use a latex-based primer on non-wood surfaces like drywall, masonry, or metal, and also on softwoods like pine. Remember, before you prime, always thoroughly degloss the surface with sandpaper. 

Bonding or priming should be carried out as soon as possible. Parts should be warmed slightly before bonding. Primers recommended include nitrile-phenolic, resorcinol-formaldehyde, vinyl phenolic, silane, and so on. Epoxies have been used on metallic surfaces, with the nylon being bonded to the epoxy. 

However, although their structures have, over the years, multiplied in number and complexity and although a considerable amount of work has been carried out in this field, the use of silanes as an accepted pretreatment or primer, prior to structural bonding in the aerospace industry, is still relatively limited 3Ms do, though, market two silane bonding primers EC 2333 and EC 3903. Certainly, they are... 

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