Silicone adhesives offer unparalleled flexibility and exceptionally high heat resistance, making them suitable for a wide range of applications in the electrical, electronic, automotive, aerospace, and construction industries.
SILICONE RUBBER USED AS AN ADHESIVE
An adhesive is a substance that is applied to the surfaces of materials to bind them together and resist separation. Adhesives are typically organized by the method of the adhesion, and they are divided into reactive or non-reactive adhesives, and of natural or synthetic origins. A polymer adhesive is a synthetic bonding substance made from different polymers (reactive or non-reactive) and is considered stronger, more flexible and has a higher impact resistance than other forms of adhesives. They are used in automotive, aerospace, aviation, construction, electronics, and electrical industries. Due to the infinite possibilities of plastic types, fillers, and additives, an adhesive can be created according to specific needs of the application with great precision. To design a good adhesive joint, some factors must be taken into account: the adhesive properties and the material information. In the first factor, cure speed, environmental resistance, thermal resistance, and suitability for automation are important. In relation to the material information, the focus is on the properties of the material that will be bonded and its surface treatments because some of them are inherently difficult to bond. For this, the surface roughening and primers are the most popular processes to improve the adhesion.
CHEMISTRY OF SILICONE ADHESIVES
Silicone adhesives are supplied as a one-part or two-part system. The first system is available to cure through moisture in the air or heat through UV or EB radiation, and the second system requires the addition of a curing agent and the mixing of the two components.
The high energy of the siloxane bonds gives silicones unique high temperature performance properties. They cure to soft thermoset elastomers with excellent property retention over a wide temperature range. The complete curing for thick sections of silicone takes a few days, but the strength may continue to increase for several weeks. This is due to the slow reaction between reactive groups on the silicone polymer and the reactive groups on the substrate surface even though the cross-linking reaction inside the silicone occurs quickly. Silicone adhesives can be categorized according to their curing reaction. The moisture curing silicones are the most important silicone adhesives. They can also be categorized by their by-product: acetoxy silicones gives off acetic acid (but promotes corrosion), oxime silicone gives off methyl ethyl ketoxime (they have lower adhesion and slower curing reaction), and alcoxy silicones give off alcohol. The latter is the best in this group because they cure rapidly and develop good adhesion to many substrates.
ADVANTAGES AND DISADVANTAGES
Silicone adhesives are easily customized and co-formulated; they have excellent electrical properties and can be formulated to be insulative with high dielectric strength or, conversely, electrically conductive. Additionally, they are biocompatible.
Although some silicone adhesives release corrosive entities, there are special formulations that are non-corrosive and chemically and thermally stable.
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