From now, the application of adhesives has penetrated into various fields of the national economy. On many occasions, adhesives can effectively replace welding, riveting, screw-joint and many other mechanical connections. Practice has shown that this method has the effects of reducing costs, increasing strength, simplifying technology, saving energy and increasing economic efficiency.
As the fast development of science and technology, higher requirements are put forward for the performance and bonding technology of adhesive. Different materials has different surface energy, in order to obtain a solid adhesive interface layer between the adhesive and the adhesive surface, the coupling agent containing reactive groups is often used to form chemical bonds with the solid surface of the adhesive. Materials that can be used as coupling agents include organosilane, titanate, phosphate esters and some organic acids; among these the silane coupling agents are the most proven and reliable.
For adhesives, good wetting of the resin to the adherend (or filler) is of paramount importance. If complete wetting can be obtained, the physical adsorption of the resin to the high-energy surface will provide bonding strength far higher than the cohesive strength of organic resin. In order to achieve full surface penetration, the resin must initially have a low viscosity and a lower surface tension than the critical tension on the inorganic surface, although all solid inorganic surfaces have a very high critical tension.
However, many hydrophilic inorganic materials that are in balance with moisture in the air are covered with a water film on the surface, which results in poor infiltration and expansion of the resin. Using silane coupling agent in adhesive can not only absorb water in surface but also can provide a higher critical tension on the inorganic surface, thus increasing the infiltration of the organic resin to the filler or adherend.
Compared with the two quite different functional group of silane coupling agent, the group Y is most important and can directly decide the application effect. Only when the group Y can react with the matrix resin can improve the bonding strength of organic adhesive. So in order to make group Y coupling with the resin, select appropriate silane coupling agent is very heavy key. When Y is non-reactive alkyl or aryl, it has no effect on polar resins, but can be used in the bonding of non-polar resins, such as silicone rubber and polystyrene. When Y is reactive functional group, such as vinyl, epoxy, the reactivity and solubility with the resin need to be pay more attention. Amino-silane coupling agents are versatile and can couple almost all kinds of resins except polyester resins.
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