ADHESIVES, GLUES AND SEALANTS
Currently the use of adhesives or glues as bonding agents between glass and other materials is widespread; in fact it is the best method of joint due the characteristics (rigid, low elongation and fragile) that possess the glass . Below there are some examples where adhesive are used to bond glass materials.
Bonding glass of front, side and rear glass of vehicles.
Bonding of windows glass to frame or structure.
As with the rest of the joints made with adhesives, the selection of suitable adhesive for proper bonding glass will depend among other factors:
Loads, stresses and elongations at which the glass must resist.
Technical and functional requirements of the joint.
Manufacturing costs and cost of materials that will use.
Environmental requirements and job security.
Due to the high elasticity or elongation presented by these glues, polyurethane adhesives are a good choice to be used with glass joints that need to transmit efforts. The main disadvantage of these adhesives is the poor resistance to ultraviolet radiation presented, so it is necessary to apply opaque coating that will prevent direct light exposure to the adhesive. On the other hand, these adhesives contain a chemical compound based on the isocyanate that is toxic to health, so it is necessary to have the necessary protective equipment to prevent and minimize their exposure during the use.
In order to ensure good adhesion and improve the life of the bond prior the application of polyurethane adhesive, some specific primes are applied to the glass. These primers are made especially to this kind of adhesives.This type of adhesives and glues are most used in the field of repair and replacement of windows in the front or in the rear of the car.
Modified Silanes adhesives
The use of modified silanes adhesives for bonding glass is spreading and expanding industrial sector as well as repair and maintenance sector, due its main advantage that resist to the action of ultraviolet light and its low toxicity in the absence of MDI compare to polyurethane adhesives.
Like polyurethane adhesives, modified silanes have an extraordinary elongation with some lower mechanical strength, this fact that must be taken into account when designing the width of the bead of adhesive.
Sometimes it is necessary to use primer before applying the adhesive, but the chemical compatibility of these adhesives with glass, modified silanes make perfect candidates for adhesive joints with glass.
Like Silane modified adhesives, silicone adhesives have a high resistance to the effects of ultraviolet light and have a high elongation and therefore they are recommended for bonding large areas of glass.
During the curing process these adhesives can emit contaminating silicones in adjacent areas, that silicones can produce problems with adhesion on these areas, another problem is that can produce a yellowing effect on the glass when using silicone adhesives with amines compounds.
Before applying the silicones adhesive is necessary to use a primer specifically designed for use on glass.
The use of these adhesives is determined by the degree of deformation to be hold by the union, due that these adhesives do not have an elongation as high as polyurethane, modified silanes or silicone adhesives, in favor of these adhesives provides a higher mechanical strength, so that less material is needed to apply, another advantage is that usually it´s not necessary to apply any primer.
The use of epoxy adhesives or glues as bonding materials for glass is constrained by the poor elongation properties that they have, that's why adhesive can be used for small areas of glass, this problem together with the yellowing phenomenon that occurs on the crystal surface by the action of amines make it inadvisable to use this type of adhesive for glass joints.
The use of cyanoacrylate adhesives has been spread worldwide by the famous Superglue, the main advantage of this type of adhesive is that they bond to a wide range of different materials, curing in a short space of time.
In contrast, these adhesives, like epoxies, have poor elongation properties, besides of not being resistant to the action of atmospheric moisture and ultraviolet light, all of this makes unwise the use of these adhesives for bonding glass.
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