Speaking of “adhesive”, many people may be at a loss, and to put it another way “glue”, suddenly realized. Professionally known as adhesives, the range of adhesives is too wide and has been widely used in aerospace, aircraft manufacturing, electronics industry, machining, automobile manufacturing, construction and medical care. Adhesives are used in everything from food, clothing, housing and transportation to aerospace. Silicone is one of them.
Silicone? What is Silicone? Organosilicon compounds refer to compounds that contain Si-C bonds and at least one organic group is directly connected to a silicon atom. It is also customary to use those compounds that connect organic groups to silicon atoms through oxygen, sulfur, nitrogen, etc. Also used as organosilicon compounds. Among them, the polysiloxane composed of silicon-oxygen bond (-Si-O-Si-) as the skeleton is the most numerous, the most deeply studied and the most widely used type of organosilicon compounds, accounting for more than 90% of the total dosage. .
The silicone adhesive is a one-component, translucent paste-like room temperature curing adhesive, which is a high-performance elastomer that is naturally cured. It has excellent heat and cold resistance, aging resistance and electrical insulation properties, and has good adhesion to most metal and non-metal materials.
Silicone adhesives can be divided into two categories: silicone resin-based adhesives and silicone rubber-based adhesives. The chemical structures of the two are different: the silicon-oxygen bond is the main chain of the body structure, which can be further condensed into a high-strength cross-linked hard and brittle resin at high temperature; while silicone rubber is a linear silicone rubber. A relatively high molecular weight elastomer with oxygen bonds as the main chain. The relative molecular weight ranges from tens of thousands to hundreds of thousands, and they must be condensed into elastomers with several cross-linking points under the action of curing agents or catalysts. It can also be divided into two types: condensation type and addition type. The addition type is a silicone adhesive made of cyanopolysiloxane and vinyl polysiloxane as the main material under the action of a catalyst.
Compared with other types of polymer materials, what are the excellent properties of silicone adhesives?
The basic structural unit of silicone products is composed of silicon-oxygen chains, and the side chains are connected to various other organic groups through silicon atoms. Therefore, the structure of silicone products contains both “organic groups” and “inorganic structures”. This special composition and molecular structure make it combine the characteristics of organic substances with the functions of inorganic substances.
Compared with other polymer materials, the most outstanding properties of silicone adhesives are:
- Temperature resistance
The silicone adhesive is based on a silicon-oxygen (Si-O) bond as the main chain structure. The bond energy of the C-C bond is 82.6 kcal/mol, and the bond energy of the Si-O bond is 121 kcal in silicone. /molecule, so the thermal stability of the silicone adhesive is high, and the chemical bonds of the molecules are not broken or decomposed under high temperature (or radiation irradiation). Silicone adhesives are not only resistant to high temperatures but also low temperatures, and can be used in a wide temperature range. Whether it is chemical properties or physical and mechanical properties, the change with temperature is very small.
- Weather resistance
The main chain of the silicone adhesive is -Si-O-, and there is no double bond, so it is not easy to be decomposed by ultraviolet light and ozone. Silicone adhesives have better thermal stability, radiation resistance and weather resistance than other polymer materials. The service life of silicone adhesives in natural environment can reach several decades.
- Electrical insulation properties
Silicone adhesives all have good electrical insulation properties, and their dielectric loss, withstand voltage, arc resistance, corona resistance, volume resistivity and surface resistivity are among the best in insulating materials, and their electrical properties are affected by temperature and frequency. impact is small. Therefore, they are a stable electrical insulating material and are widely used in the electronics and electrical industries. In addition to excellent heat resistance, silicone adhesives also have excellent water repellency, which enables electrical equipment to be used in wet conditions with high reliability.
- physiological inertia
Polysiloxanes are among the most inactive compounds known. They are very resistant to biological aging, have no rejection reaction with animals, and have good anticoagulant properties.
- Low surface tension and low surface energy
The main chain of the silicone adhesive is very flexible, and its intermolecular force is much weaker than that of hydrocarbons. Therefore, it has lower viscosity, weaker surface tension, lower surface energy, and stronger film-forming ability than hydrocarbons of the same molecular weight. This low surface tension and low surface energy are the main reasons for its many applications: hydrophobicity, defoaming, foam stabilization, anti-sticking, lubrication, glazing and other excellent properties.
It is these excellent properties of silicone adhesives that are widely used in military/aerospace/construction/electrical/electronics/automobile/leather/textile/chemical/medical and medical industries.