Adhesives are needed everywhere in life, so what is adhesives? Adhesives are usually defined as: through the adhesion of the interface and the cohesion of the substance, which can make two or more kinds of natural or synthetic, organic or inorganic substances connected together, collectively referred to as adhesives (adhesive), also called adhesives, commonly known as glue. Today, we will talk about the characteristics and applications of different types of adhesives.

Silicone adhesive

Organic silicone adhesives include two categories of adhesives (including sealants) based on silicone resin or silicone elastomer.
Silicone resin is composed of a spatial network structure of Si-O-Si main chain. It is a cross-linked semi-inorganic polymer connected with organic groups on silicon atoms, and can be further condensed into a highly cross-linked hard and brittle resin at high temperature.

Silicone rubber is a linear polysiloxane with Si-O-Si as the main chain (molecular weight ranging from tens of thousands to hundreds of thousands), in the curing agent and catalyst to form a number of crosslinking points of the elastomer, by polydimethylsiloxan-based silicone rubber, also known as silicone rubber.

The former is mainly used for bonding metal and heat-resistant non-metallic materials, the obtained adhesive parts can be used in a temperature range of 60 ~ 250 ° C, the latter is mainly used for bonding heat-resistant rubber, rubber and metal and other non-metallic materials, generally can be used at a 60 ~ 200 ° C.

Organic silicone adhesives can be roughly divided into pure organic silicone adhesives and modified organic silicone adhesives. Pure organic silicone adhesive is mainly composed of active polysiloxane (hydroxy-terminated silicone rubber, containing hydrogen or vinyl silicone oil), curing agent, catalyst, filler and auxiliary.

According to the difference of curing reaction, it can be divided into condensation type, free radical initiation type and silane addition type. According to the different composition and function, it can be divided into one-component silicone, two-component silicone and silicone pressure sensitive adhesive.

Because of its own molecular structure, the organic silicone adhesive has many superior properties, with cold resistance, heat resistance, aging resistance, waterproof, moisture-proof, high tensile fatigue strength, small permanent deformation, non-toxic and so on. In recent years, such adhesives have developed rapidly in China. At present, it has been widely used in electronic appliances, aerospace, construction industry and other fields.

Polyurethane adhesive

Polyurethane adhesive refers to the adhesive containing carbamate group or isocyanate group in the molecular chain. According to the reaction composition, it can be divided into polyisocyanate adhesive, polyurethane adhesive containing isocyanate group, polyurethane adhesive containing hydroxyl and polyurethane resin adhesive.

Polyurethane adhesive has strong adhesion, large initial adhesion and wide application range. Because the -NCO in the molecular chain of polyurethane adhesives can react with a variety of functional groups containing active hydrogen to form interfacial chemical bonds, it has strong adhesion properties to a variety of materials. It can not only bond porous materials, such as foam, ceramics, wood, fabrics, etc., but also bond a variety of metals, inorganic materials, plastics, rubber and leather, etc., which is a wide range of adhesives.

Outstanding low temperature resistance is also its unique feature. At very low temperatures, general polymer materials are converted into glass state and become brittle, and polyurethane adhesives can maintain a high peel strength even below -250℃, while its shear strength increases significantly with the decrease of temperature.