What types of adhesives are commonly used in industry?

1. Epoxy adhesive base mainly uses epoxy resin, and the most widely used in China is bisphenol type A, commonly known as "universal glue".

Epoxy adhesive is a curing system with high temperature resistance, good toughness and high reactivity formulated by polyurethane prepolymer modified epoxy resin (component A) and self-made curing agent (component B) in a ratio of 10∶1~1∶1 (weight ratio). The polyurethane prepolymer is a polysiloxane polyurethane prepolymer with a certain proportion of hydroxyl polysiloxane and diisocyanate reacting under certain conditions to form an isocyane polyurethane prepolymer with the end of the isocyanate group, and then the polyurethane prepolymer is used to modify the epoxy resin. The homemade curing agent is composed of diamines, imidazoles, silane couplings, inorganic fillers and catalysts.

2. Modified phenolic adhesive has good heat resistance, aging resistance, and high bonding strength, but is brittle and has a large curing shrinkage.

Modified phenolic adhesives are adhesives obtained by using toughening agents to improve the properties of phenolic resins. Modified Phenolic (Resin) Adhesive adhesive is an adhesive obtained by improving the properties of phenolic resins with toughening agents. Phenolic resin has excellent heat resistance, but is brittle. The addition of toughening agents can improve brittleness and maintain its heat resistance. The main ones are phenolic, polyvinyl alcohol acetal adhesives, phenolic-silicone resin adhesives and phenolic-rubber adhesives.

3. Polyurethane adhesive has good flexibility and can be used at low temperatures, but it is not heat-resistant and has low strength.

Polyurethane adhesives refer to adhesives that contain carbamate groups (-NHCOO-) or isocyanate groups (-NCO) in their molecular chains. Polyurethane adhesives are divided into two categories: polyisocyanates and polyurethanes. Polyisocyanate molecular chains contain isocyanide (-NCO) and carbamate group (-NH-COO-), so polyurethane adhesives exhibit high activity and polarity. It has excellent chemical adhesion to substrates containing reactive hydrogen, such as foam, plastic, wood, leather, fabric, paper, ceramics and other porous materials, as well as metal, glass, rubber, plastic and other materials with smooth surfaces.

4. α-cyanoacrylate adhesive is a fast-curing adhesive at room temperature, also known as "quick-drying adhesive", but it has poor heat resistance and solubility resistance.

Cyanoacrylate is an acrolein-based resin, when the super glue is applied to the surface of the object, the solvent will evaporate, and the water on the surface of the object or from the air (more precisely, the hydroxide ions formed by the water) will cause the monomer to quickly carry out anionic polymerization (anionic polymerization) to form a long and strong chain that sticks the two surfaces together. Since its polymerization process is an exothermic reaction, it can be found that its temperature rises slightly. Since the solvent (acetone) evaporates in between, the use of super glue will smell some unbearable odors.

5. Anaerobic glue This is a kind of glue that cannot be cured when it is aerobic at room temperature, but can cure quickly when oxygen is expelled. The main component is the diester of methacrylic acid.

Anaerotic adhesive (anaerotic adhesive) is referred to as anaerobic adhesive, also known as anaerobic adhesive, aerobic adhesive, thread adhesive, mechanical adhesive, also known as "anaerobic locking (tightening) agent abroad", is a new type of sealing adhesive. It will not solidify when it comes into contact with oxygen or air, and once it is isolated from the air, coupled with the catalytic action of the metal surface, it can quickly polymerize and cure at room temperature, forming a strong bond and a good seal. By using the polymerization inhibition effect of oxygen, it can be stored for many years.

A one-component adhesive that remains liquid in the presence of air at room temperature and cures quickly when air is isolated. Curing at room temperature, the volume shrinkage is relatively small during curing (because there is no solvent), good heat resistance, chemical resistance, vibration resistance, impact resistance (compared with screws and spring pads), stable storage (1 year at room temperature), easy automatic operation, non-curing of overflowing parts, easy to clean. It is especially suitable for screw and threaded parts fastening, shaft fixing, flange sealing, fine hole sealing, impregnation, structural gluing, etc. The main component of anaerobic glue is (methyl)acrylate, and the commonly used initiators are cumene hydroperoxide or tert-butyl hydroperoxide, accelerators (such as saccharin, benzenesulfonylhydrazine), and stabilizers, polymerization inhibitors and modifiers are also added. Recently, pressure-sensitive anaerobic adhesives, high-temperature anaerobic adhesives, strong anaerobic adhesives, UV-curable anaerobic adhesives, etc. have been developed.

6. Inorganic adhesive can be used at 1300°C, with high bonding strength but brittleness.

Inorganic adhesives are a new type of adhesive. It can withstand both high and low temperatures, low cost, not easy to age, simple structure, and high adhesion.

The high temperature that general organic adhesives can withstand is usually below 100°C. For example, latex is below 60°C, epoxy resin is about 100°C, phenolic resin is about 220°C. Inorganic adhesives can withstand high temperatures of 600-900°C,[1] and more than 1800°C after improving the composition.

Someone once soaked an item bonded with inorganic adhesive in liquid oxygen at -186°C, and the bonding effect did not change. There is a copper phosphate inorganic glue, the main components are aluminum phosphate solution and copper monoxide powder. After applying this glue, the surface will become very rough and staggered, which will make the tensile strength of the item 3-5 times higher than that of flat items. Inorganic adhesives are used for bonding rocket and spacecraft parts, low-temperature surgical instruments, automobile and ship engines, oxygen concentrator parts, bonding and repairing, etc.