According to statistics, each passenger car in my country currently uses approximately 20 kg of adhesive, a mid-sized car about 16 kg, and a heavy-duty car about 22 kg. By 2020, the total demand for various adhesives and sealants in my country's automotive industry will reach 300,000 tons. This article discusses the recent development of adhesives used in automobiles, including the bonding areas and characteristics of the vehicle body, operating system, powertrain, and repair systems, along with the types and main properties of the adhesives used.

Automotive Interior Adhesives

Chloroprene Decorative Adhesives

Chloroprene rubber is the earliest developed synthetic rubber. It exhibits reversible crystallization, high bonding strength, high tensile strength and elongation, and excellent weather and heat resistance. The resulting adhesive can be cold-cured at room temperature and exhibits high bond strength, high initial tack, good media resistance, and a wide bonding range. However, long-term storage of chloroprene rubber releases hydrogen chloride, which promotes hydrolysis and corrosiveness to metals. Therefore, magnesium oxide and light zinc chloride are added to the adhesive. Anti-aging agents can also be added to prevent adhesive aging.

Adhesives for Automotive Ceiling Lighting

EVA Hot Melt Adhesive

Currently, the most widely used hot melt adhesive. It uses EVA resin as a base, tackifiers include rosin glycerol esters, polymerized rosin, and plasticizers such as high-molecular paraffin wax.

Sealants for Automotive Body Structures

PU adhesives contain urethane (NHCOO) and/or isocyanate (NCO) groups in their base molecules. They are the most commonly used sealants, offering excellent wear resistance, adjustable performance, a wide range of applications, high mechanical strength, low-temperature flexibility, and excellent recovery properties. They can be used for sealing dynamic joints. However, they also have disadvantages, such as poor long-term heat resistance, susceptibility to UV aging, and the need for a primer in many applications. Polyurethane sealants are used in automotive applications such as window (windshield) assembly and sealing, and assembly of vehicle bodies and other components. In recent years, annual demand for polyurethane adhesives in my country has grown at an average rate of 30%. Other sealants include rubber-based and polysulfide sealants.

Adhesives for Automotive Running Systems

Bonding in automotive running systems primarily involves the bonding of friction pads and clutch plates. These adhesives require high bond strength, excellent heat resistance, and a certain degree of toughness, while also being low-cost and offering good processability.

Adhesives for automotive running systems primarily use modified phenolic resin adhesives for brake pad bonding. Drum brake pad adhesives bond the manufactured brake pads to the steel backing, typically using a nitrile rubber-modified phenolic resin adhesive. Disc brake pad adhesives are made by pressing brake pad powder into a cold blank and applying adhesive. The blank is then positioned with the coated steel backing at high temperature for a short period of time, followed by post-processing at high temperature without pressure. Currently, disc brake pad adhesives used in China are prepared using calcium oxide as a catalyst. In addition to the above adhesives, silicone-modified phenolic resins can also be used for clutch bonding.

Adhesives for Automotive Powertrains

Bonded areas in automotive powertrains primarily include the tightening and sealing of screws and bolts, and the sealing of cylinder gaskets. Anaerobic adhesives are widely used in the automotive manufacturing industry for thread fastening and locking, securing mating parts, bonding surfaces, sealing pipes and flanges, and sealing pinholes. They prevent loosening and leaks, simplifying the assembly process.

Various types of anaerobic adhesives are primarily used to remove sand holes generated during engine casting, tighten various bolts, seal pipes, and seal surfaces in automotive powertrains. Sand holes generated during engine casting are poorly sealed using water glass impregnation, while high-temperature resistant anaerobic adhesive impregnation can achieve excellent sealing results. High-strength anaerobic adhesives are suitable for securing and sealing engine cylinder heads and transmission studs, as well as bolts that are frequently disassembled, such as assemblies, cylindrical bowl-shaped plugs, drive axle differential case connecting bolts, and round shaft gear and differential fixing bolts. In addition, automotive gaskets cannot guarantee the sealing performance and geometric accuracy of the connecting parts, but the use of anaerobic adhesives for plane sealing can solve these problems. Low-strength anaerobic adhesives can be used for parts that are easy to disassemble.