Лако-красочные материалы — производство

It has been emphasised that the achievement of a high standard of surface pretreatment is the key to maximising joint durability and joint quality. Unfortunately, in the practice of adhesive bonding for applications in construction, surface pretreatment is likely to be the most difficult process to control. The choice and specification of pretreatment procedures should be influenced mainly by the required durability and, ideally, should entail simple reproducible processes. However the location and scale of operations, the nature of the adherends, the adhesive to be used, the safety and environmental aspects, and of course the cost, all have to be taken into consideration. The performance of joints constructed with cold-cure epoxides is likely to be critically dependent upon surface preparation. Some heat-cured products, notably the acrylics and epoxies, are claimed to be tolerant of oily and greasy surfaces, but their use should not be seen as an alternative to good surface preparation bearing in mind the usual civil engineering long term durability requirements. The stability of the adherend/adhesive interface is probably the most important factor in the durability of bonded joints.

Some materials can create particular problems for surface prep­aration and for obtaining adequate adhesion, and so should be avoided if possible. Bonds to metal alloys and plastics have been well researched, and a number of procedures are documented. Bonds to cementitious and siliceous surfaces are also readily obtainable, although little is really known about optimising surface treatment processes for maximum adhesion. Regard should be paid to the dusty, friable nature of concrete surfaces, as well as its high alkalinity.

For mild steel adherends, gritblasting is likely to be the minimum appropriate pretreatment. Careful specification of rust removal and degreasing procedures prior to blasting is necessary, as is the identification of the type of grit, pressure of blasting, and so on. For stainless steels, a non-ferrous grit such as alumina should be employed. Following blasting dust removal is desirable (e. g. by brushing or blowing), but further degreasing is not advised. The chemical etching of concrete is likely to lead to many problems unless the necessary procedures are carried out to the letter of a detailed specification; any chemical residues will cause long term durability problems at the adherend/adhesive interface.

The use of adhesive primers may be more important in some instances than others (e. g. on porous surfaces). Experience has shown that, despite the extra process involved, the advantages to be gained by priming in terms of presenting a reproducible surface to the adhesive far outweigh the possible disadvantages. Their use may also negate the need for complex surface pretreatment procedures. Certain siloxane coupling agents have been shown to provide a significant increase in joint durability, as have corrosion- inhibiting primers. Compatibility with the adhesive must of course be first established.

The control of surface pretreatment procedures may be done optically, by assessment of surface wettability, by surface analytical means, or by the use of simple mechanical test procedures. (See ‘Adhesion control’.)