Technology Application | Let's Learn About Two Different Types Of Adhesives

Adhesives are needed everywhere in life, so what exactly are adhesives? Adhesives are usually defined as a class of natural or synthetic, organic or inorganic substances that can connect two or more parts or materials together through interface adhesion and material cohesion. They are collectively called adhesives, also known as adhesives, and are usually called glue. Today, let's talk about the characteristics and applications of two 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 with Si-o-Si as the main chain. It is a cross-linked semi-inorganic polymer with organic groups connected to silicon atoms. It 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). It is an elastomer that forms several cross-linking points under the action of curing agent and catalyst. Silicone rubber mainly composed of polydimethylsiloxane is also called silicone glue.

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

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

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

Due to its own molecular structure, silicone adhesive has many superior properties, such as cold resistance, heat resistance, aging resistance, waterproof, moisture resistance, high telescopic fatigue strength, small permanent deformation, and non-toxicity. In recent years, this type of adhesive has developed rapidly in China. At present, it has been widely used in the fields of electronics, aerospace, and construction industry.

Polyurethane Adhesive

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

Polyurethane adhesives have strong bonding strength, large initial adhesion and a wide range of applications. Since 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 extremely strong adhesion to a variety of materials. It can not only bond porous materials such as foam plastics, ceramics, wood, fabrics, etc., but also a variety of metals, inorganic materials, plastics, rubber and leather, etc. It is an adhesive with a wide range of applications.

Outstanding low temperature resistance is also its unique feature. At extremely low temperatures, general polymer materials are converted into glassy state and become brittle, while polyurethane adhesives can still maintain a high peel strength even below -250°C, and its shear strength increases significantly as the temperature decreases.

Polyurethane adhesives are mainly used in the fields of shoemaking, packaging, automobiles, magnetic recording materials, etc.