Humans have used adhesives for thousands of years. However, epoxy resin adhesive (abbreviated as epoxy adhesive or epoxy adhesive) began to appear around 1950, with a history of only over 50 years. However, with the introduction of various adhesive theories in the mid-20th century, and the in-depth progress of basic research work such as adhesive interface chemistry, adhesive rheology and adhesive failure mechanism, the properties, varieties and applications of adhesives have developed by leaps and bounds.
Epoxy resin and its curing system have become a kind of important adhesives with excellent properties, various varieties and wide adaptability because of their unique and excellent properties and the continuous emergence of new epoxy resins, new curing agents and additives. Epoxy adhesive was once called "all-purpose adhesive" and "super adhesive" because of its high bonding strength and versatility. It has been widely used in aviation, aerospace, automobile, machinery, architecture, chemical industry, light industry, electronics, electrical appliances and daily life.
Epoxy adhesive is a liquid or solid adhesive composed of epoxy resin, curing agent, accelerator, modifier, diluent and filler. The bonding process of epoxy adhesive is a complex physical and chemical process, including soaking, bonding, curing and other steps. Finally, a cured product with three-dimensional cross-linking structure is generated, which is integrated with the adherend. Bonding performance (strength, heat resistance, corrosion resistance, impermeability, etc. ) not only depends on the structure and performance of the adhesive, but also on the surface structure and bonding characteristics of the adherend, and is closely related to the joint design, preparation and storage of the adhesive and bonding technology, and is also restricted by the surrounding environment (stress, temperature, humidity, medium, etc.). ).
Therefore, the application of epoxy adhesive is a systematic project. The performance of epoxy adhesive must adapt to the above factors that affect the bonding performance in order to obtain the best effect. When epoxy adhesive with the same formula is used to bond objects with different properties, or different bonding conditions are used, or in different use environments, its properties will be very different. Full attention should be paid to application.
There are many kinds of epoxy resin adhesives, but the classification method and index have not been unified. According to the reporter of China Epoxy Resin Industry Online (www.epoxy-e.cn), it is usually classified according to the following methods.
First of all, according to the form of adhesive classification. Such as solvent-free adhesives, (organic) solvent-based adhesives, water-based adhesives (which can be divided into water-emulsion adhesives and water-soluble adhesives), paste adhesives, and film adhesives (epoxy films).
Second, according to the maintenance conditions. (1) Cold curing adhesive (curing adhesive without heating). It is also divided into: low-temperature curing adhesive with curing temperature < 15℃; Room temperature curing adhesive, curing temperature 15-40℃. (2) Thermosetting glue. It can also be divided into: moderate temperature curing glue, the curing temperature is about 80-120℃; High temperature curing adhesive, curing temperature > 65438 050℃. (3) Curing glue in other ways, such as light curing glue, wet surface and water curing glue, latent curing glue, etc.
Three, according to the bond strength classification. Structural adhesive (1) has high shear and tensile strength and high uneven tear strength, so that the bonded joint can withstand vibration, fatigue and impact for a long time. At the same time, it should also have high heat resistance and weather resistance. Generally, the room temperature shear strength of steel-steel is greater than 25MPa, and the tensile strength is greater than or equal to ≥33MPa. Uneven tear strength > 40kn/m (2) Secondary structural adhesive can bear moderate load. General shear strength is 17-25mpa, and uneven tear strength is 20-50kn/m (3) Non-structural adhesive, that is, all-purpose adhesive. Its room temperature strength is still relatively high, but with the increase of temperature, the bonding strength decreases rapidly. Can only be used for parts with little stress.
Fourth, classify by purpose. (1) all-purpose adhesive. (2) Special adhesive. Such as high temperature resistant adhesive (service temperature ≥ 150℃), low temperature resistant adhesive (temperature -50℃ or lower), strain adhesive (used to attach strain gauges), conductive adhesive (volume resistivity10-3 ~/kloc-0-4 Ω cm), and sealant (.
In addition, it can be classified according to the types of curing agents, such as amine cured epoxy adhesive and anhydride cured adhesive. It can also be divided into two-component adhesive and one-component adhesive, pure epoxy adhesive and modified epoxy adhesive (such as epoxy-nylon adhesive, epoxy-polysulfide rubber adhesive, epoxy-nitrile rubber, epoxy-polyurethane adhesive, epoxy-phenolic adhesive, silicone epoxy adhesive and acrylic epoxy adhesive).