The preparation of the glass surfaces is intended primarily to improve the wetting properties and adhesion of the glass surface.
Glass is a transparent material, hard, tough and fragile because of its characteristics, it is used in a large number of products we use daily such as glasses, bottles, windows, lens etc. ..
Silicon oxide is the main chemical compound of glass, approximately 72% of ordinary glasses are made of silicon oxide (SiO2). During the manufacture of glass, compounds and additives added as carbonates, sulfates and nitrates of sodium and potassium, which improve the liquefaction of the glass.
The water presented in the environment as moisture reacts slowly with nitrates, carbonates and sulfates of sodium and potassium and produce form sodium and potassium hydroxide, also the moisture it reacts with silicon oxide the breaking inside structures of glass, it can produce a cracking of the material on the surface.
The set of hydroxides of sodium, potassium and silicon formed in the outer layer of glass is called gel layer, which has a low surface energy and high instability, resulting in a poor wetting and dismal adherence to any adhesive.
A proper and accurate surface preparation of the glass allows us to eliminate the gel layer that is formed naturally on the surfaces of the glass.
Generally is not recommended the use of mechanical or chemical techniques such as blasting, sanding or etching in the glass as surface preparation, due they may cause microcracks on the surface and may reach the breaking of the glass.
Usually a good cleaning with organic solvents for a short time and with the help of adhesion promoters, primers and / or activators are enough to generate a fresh active surface of the glasses.
Polyurethane adhesives, silicones and silanes modified / hybrid polymer adhesives are generally used for adhesive bonding with glass, owing to their elongation. You can find glass adhesive joints with acrylate adhesives, these adhesives are reformulated especially for the use of glass, providing more elongation and removing certain compounds that can cause the yellowing of the glass.
In case that the adhesive joint is exposed to the outside, the transparency of glass allows UV light to pass through, so it is necessary to protect the adhesive, such as using black primer in order to prevent aging of the adhesive union and adhesive itself, that effect occur in polyurethanes adhesives, silanes modified adhesives are very resistant to U.V. compare with polyurethanes.