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.

Polyurethane adhesives are mainly used in footwear, packaging, automobiles, magnetic recording materials and other fields.

Polyacrylic resin

Acrylic resin adhesive is a class of acrylic adhesive, made of acrylic resin, need to cure in the absence of air. It is often used for sealing, screw connection and fastening of adhesive rotating bearings. The disadvantage is that the heat resistance is not high enough, the curing time is long, and it is not suitable for sealing with large gaps.

It is mainly used in the production of pressure sensitive adhesives, and is also used in the textile and construction fields.

Hot melt adhesive
Hot melt adhesive is short for hot melt adhesive, it does not use any solvent in production and application, non-toxic, tasteless, does not pollute the environment, known as "green adhesive", especially suitable for use in continuous production lines. Hot melt adhesive is a kind of polymer adhesive which is coated in hot melt state and bonded by cooling hardening. According to the provisions of the national standard, the definition of hot melt adhesive is "a thermoplastic adhesive that is coated in a molten state and cooled into a solid state to complete the bonding". Solvent-free, 100% solid content, mainly composed of thermoplastic polymer. Hot melt adhesive from the late 1950s began to be applied to packaging, due to its own unique advantages, compared with other adhesive varieties have incomparable advantages, become one of the fastest growing varieties of adhesives. According to different raw materials, it can be divided into EVA hot melt adhesive, polyamide hot melt adhesive, polyester hot melt adhesive, polyolefin hot melt adhesive and so on. At present, the main domestic production and use of EVA hot melt adhesive. The main raw materials of polyolefin adhesives are ethylene series, SBS and SIS copolymers.

Epoxy resin adhesive
Epoxy resin adhesives (referred to as epoxy adhesives or epoxy adhesives) have been around since 1950, only more than 50 years.
However, with the successive introduction of various adhesive theories in the middle of the 20th century, as well as the in-depth progress of basic research work such as adhesive chemistry, adhesive rheology and adhesive failure mechanism, the properties, varieties and applications of adhesives have been developed by leaps and bounds.
Epoxy resin and its curing system also with its unique, excellent performance and the continuous emergence of new epoxy resin, new curing agent and additives, become an important class of adhesive with excellent performance, many varieties and wide adaptability.
It can be used for bonding between metal and most non-metallic materials, and is widely used in construction, automobiles, electronics, electrical appliances and daily household goods.

Ureate resin
Urea-formaldehyde resin is also called urea-formaldehyde resin. English abbreviation UF, urea and formaldehyde under the action of a catalyst (alkaline or acidic catalyst), condensation into an initial urea-formaldehyde resin, and then under the action of curing agents or additives, the formation of insoluble, non-melting late thermosetting resin.
The cured urea formaldehyde resin color is lighter than phenolic resin, translucent, weak acid, weak alkali resistance, good insulation performance, excellent wear resistance, cheap price, it is the largest amount of adhesive varieties. Especially in the manufacture of various wood-based panels in the wood processing industry, urea-formaldehyde resin and its modified products account for about 90% of the total amount of adhesives.
It is mainly used in the wood processing industry, but the formaldehyde release after use is higher than the international standard.

Source: Internet Synthesis
Disclaimer: The content is from the Internet, wechat public accounts and other public channels, we maintain a neutral attitude towards the opinions in the article. This article is for reference only, communication. The copyright of the reproduced manuscript belongs to the original author and the institution, if there is infringement, please contact us to delete.