Development Status and Prospects of Automotive Adhesives

The history of automotive adhesives is almost as long as the automotive industry itself. With the improvement of the performance, manufacturing, and application technology of automotive adhesives, the automotive industry has become the largest application field of adhesives, second only to construction and light industry, covering almost all types of adhesives, and the application range is becoming wider and wider, and the proportion of vehicle usage is also increasing.

Automotive adhesives must meet the lifespan requirements of the vehicle under harsh conditions, including temperature resistance, salt water resistance, fuel resistance, oil resistance, high temperature resistance, vibration resistance, impact resistance, detergent resistance, and dust resistance. The application of adhesives can improve driving comfort, reduce noise, reduce vibration, reduce mass, reduce energy consumption, simplify processes, improve product quality, and achieve effects that are difficult to achieve by other connection methods.

1、 Development background and current situation of automotive adhesives

In 1979, the automotive industry first invited Japanese companies to China to discuss the technology of automotive adhesives. Some specialized adhesives for automobiles, such as epoxy adhesive, liquid sealant, PVC melt adhesive, polyurethane adhesive, etc., were developed during this period.

After the 1980s, the introduction of automotive technology led to greater development in the adhesive sealing industry, and a batch of new and more specialized adhesives were developed during the localization process of automotive materials. For example, anaerobic adhesive series products, shockproof and heat insulation film, wear-resistant silicone adhesive, automotive ceiling adhesive, carpet adhesive, weld adhesive, double-sided adhesive tape, potting adhesive, etc. are included in this list. At the same time, some larger and more specialized adhesive factories have also been established, such as Letai (China) Company, Henkel Surface Technology Changchun Company, Shandong Kane New Material Technology Co., Ltd. Currently, except for a very small number of adhesives used in automobiles, a corresponding part has already been domestically produced.

2、 Application classification of automotive adhesives

1. Adhesives for automotive body

The bonding parts of the car body structure include the bonding and sealing of the body, roof, doors, and seats.

1.1 Adhesives for automotive body

（1） Acrylate type pressure sensitive adhesive: Pressure sensitive adhesive refers to an adhesive that can generate bonding force through appropriate pressure. This adhesive has a certain bonding force on various materials and has high peel strength, and can even be reused. Acrylate pressure-sensitive adhesive is a copolymer of acrylic acid. This adhesive has a simple formula and does not require thickeners, softeners, or antioxidants. It is non-toxic or low toxic, and its long-term outdoor performance does not decrease significantly. Therefore, it has become the largest variety in the field of pressure sensitive adhesive production.

（2） SBS type pressure sensitive adhesive: The main raw materials are SBS and SIS, which are rarely used.

1.2 Adhesives for Automotive Interior

（1） Chloroprene decorative adhesive

Neoprene is the first developed synthetic rubber, which has reversible crystallinity, high adhesive strength, high tensile strength and elongation, excellent weather resistance and heat resistance. The prepared adhesive can be cold cured at room temperature, and has the characteristics of high adhesive strength, high initial adhesion, good medium resistance, wide bonding range, etc. However, long-term storage of Neoprene will release hydrogen chloride, promote its hydrolysis, and corrode metals. Therefore, magnesium oxide and light Zinc chloride need to be added. In order to prevent the aging of adhesive, antioxidant can also be added.

（2） SBS decorative adhesive

It has the characteristics of high strength, good toughness, fast curing, and low temperature resistance.

（3） Water-based decorative adhesive

High solid content, with good bonding strength.

In addition, there is polyurethane adhesive.

1.3 Adhesives for automotive ceiling lighting fixtures

（1） EVA Hot-melt adhesive

At present, the largest amount of Hot-melt adhesive is used. Using EVA resin as the base material, the tackifier is rosin glycerol ester, polymerized rosin, etc., and the plasticizer is polymer paraffin, etc.

（2） SBS Hot-melt adhesive

It is similar to EVA Hot-melt adhesive in composition, but SBS is used instead of EVA to obtain Hot-melt adhesive with different properties.

In addition, there are polyamide Hot-melt adhesive and polyester Hot-melt adhesive.

1.4 Sealing adhesive for automotive body structure

PU adhesive is an adhesive that contains amino ester groups (NHCOO) and/or isocyanate groups (NCO) in the base material molecules. It is the most commonly used sealant with good wear resistance, adjustable performance, wide application range, high mechanical strength, low tenderness and softness, and excellent resilience. It can be used for sealing dynamic joints. But there are also drawbacks, such as not being able to withstand long-term heat, being susceptible to UV aging, and requiring a primer in many situations. The application of polyurethane sealant in automobiles includes the assembly and sealing of car windows (windshields), and the assembly of vehicle bodies and other components. In recent years, the annual demand for polyurethane adhesives in China has increased at an average rate of 30%. In addition, there are rubber type sealing adhesives and polysulfide sealing adhesives.

1.5 Welding Sealant

Pre coating on the overlapping parts of steel plate welding, spot welding, and filling the gaps to ensure sealing and prevent rusting. Spot welding sealant is even more indispensable for areas that are obscured after assembly and difficult to apply weld sealant. This kind of adhesive mainly includes resin type sealant based on PVC weld sealant and rubber type welding sealant based on styrene butadiene and Butyl rubber.

2. Adhesives for automotive operating systems

The bonding of automotive operating systems mainly includes the bonding of friction plates and clutch plates. This type of adhesive requires high bonding strength, excellent heat resistance, and a certain degree of toughness, as well as low cost and good process performance.

The main adhesive used for automotive operating systems is modified phenolic resin adhesive for brake pad bonding. Drum brake pad adhesive is used to bond the manufactured brake pad and steel back together, usually using nitrile rubber modified phenolic resin adhesive. Disc brake pad adhesive is to press the brake pad powder into cold embryo and apply glue, then position it with the steel back after gluing for a short time at high temperature, and then conduct post-treatment under high temperature and no pressure. At present, disc brake pad adhesive prepared with Calcium oxide as catalyst is used in China. In addition to the above adhesives, the adhesive used for the clutch can also be bonded with silicone modified phenolic resin.

3. Adhesives for automotive power systems

The bonding parts of the automotive power system mainly include the fastening and sealing of screws and bolts, as well as the sealing of cylinder gaskets. In the automotive manufacturing industry, anaerobic adhesives are more commonly used for thread fastening and locking, fixing of mating parts, plane bonding, sealing of pipelines and flanges, and needle hole sealing, which can solve problems such as looseness and leakage prevention, and simplify the assembly process.

Various types of anaerobic adhesives are mainly used for the sand holes generated during engine casting in the automotive power system, fastening of various bolts, sealing of pipelines, and flat sealing. The sand holes generated during engine casting are poorly sealed by water glass infiltration, while using high-temperature resistant anaerobic adhesive infiltration can achieve good sealing effect. High strength anaerobic adhesive can be used for fixing and sealing engine cylinder heads and gearbox double head bolts, as well as infrequently disassembled bolts, collective process bodies, cylindrical bowl shaped plug drive axle differential case connecting bolts, circular shaft gear and differential fixing bolts, etc. In addition, automotive gaskets cannot guarantee sealing performance and geometric accuracy of connecting components, and using anaerobic adhesive for flat sealing can solve these problems. Components that are easy to disassemble can use low strength anaerobic adhesive.

4. Adhesive for automotive repair

In automotive maintenance, various new adhesives are widely used for repairing corrosion, wear, abrasions, and defects in automobiles, as well as for thread locking, flat sealing, pipeline thread sealing, cylindrical component fixation, etc., thereby extending the service life of automobiles, ensuring their normal operation, and reducing accessory consumption and maintenance costs.

For stressed structural parts such as plates and bars, epoxy adhesive, phenolic nitrile adhesive, etc. can be used; For thin sheet metal and requiring elastic adhesive film, chloroprene adhesive can be used; The fastening, sealing, and leakage prevention of screws and nuts can be achieved with anaerobic adhesive; Cyanopropionate adhesive can be used when small areas require quick bonding. According to the different properties of the non-metallic materials adhered, such as elasticity, linear expansion coefficient, and shrinkage, rubber type, epoxy, acrylic ester, and polyurethane adhesives can be selected. When bonding plastics, adhesives should be selected according to whether they are thermosetting or thermoplastic. Thermosetting plastics can be used with adhesives such as epoxy and polyurethane; Unshaped plastics in thermoplastic plastics can be bonded with solvents, while crystalline plastics can be bonded with adhesives such as epoxy and polyurethane.

3、 Search for the Development Prospects of Automotive Adhesives

The continuous application of new materials and processes in China‘s automotive industry has promoted the continuous improvement and specialization of automotive adhesives. The application of adhesives in vehicle manufacturing is very important, and the scope of application is constantly expanding, and the dosage is also increasing. With the development of automobiles towards environmental protection, energy conservation, safety and comfort, lightweight, low cost, long lifespan, and pollution-free directions, the development and application of new high-quality automotive adhesives will become increasingly important.

Due to the early start of foreign adhesive brands, they have strong advantages in market share and product technology. In the mid to high end adhesive market, foreign brands currently have a significant competitive advantage upstream. With the strong support of national industrial policies, the R&D level of domestic adhesive enterprises has significantly improved in recent years, and the Import substitution industrialization effect of domestic brand adhesive products will become more apparent.