1. Windshield glass glue

Windshield glue refers to the fixed seal between the window glass and the body, also known as sealant.

One-component moisture-curing polyurethane sealants are commonly used today. Automotive windshields now use almost 100 percent of one-component moisture-curing polyurethane adhesives. This type of adhesive structure contains active NCO groups, which can react with trace moisture in the air when exposed to air; when bonding, it can interact with the water absorbed on the surface of the substrate and the active hydrogen groups such as hydroxyl groups present on the surface. The group undergoes a chemical reaction to form a urea bond structure. Therefore, the composition of the adhesive layer after curing of the moisture-curable polyurethane adhesive is a polyurethane-polyurea structure. Commonly used polyols for the preparation of moisture-curable polyurethane adhesives are polyether polyols and polyester polyols. The molecular weight of polyols is usually between 500-3000.

Commonly used isocyanates are MDI, TDI, HDI, IPDI, etc. The NCO content of moisture-curing adhesives is usually between 2% and 10%. The main chain of polyester polyol is a COO bond, which has a large polarity and a relatively strong cohesive force, and because of the large cohesive energy of this bond, the polyester adhesive has good high temperature resistance and oil resistance. However, since this bond is easily hydrolyzed, the hydrolysis resistance of the polyester-type urethane adhesive material is not ideal. The main chain of the polyurethane resin synthesized from polyether polyol contains ether bond structural units, which belong to a flexible chain, and the ether bond is not easy to be hydrolyzed, so it has better flexibility, hydrolysis resistance and better performance than the corresponding polyester polyol. Low temperature resistance. However, the polarity of the ether bond is not as good as that of the ester bond, and its cohesion and high temperature resistance are not as good as that of polyester polyurethane adhesives.

Therefore, most of the current research on one-component polyurethane adhesive prepolymers focuses on how to overcome the shortcomings of single-component prepolymer adhesives and obtain one-component moisture-curing polyurethane adhesives with high comprehensive performance.

Of course, in addition to the performance of the glue itself, the construction process also has a greater impact on its final performance. The construction process includes preparations before construction (environmental ventilation and cleaning conditions, tools used, etc.) → cleaning and activation → primer coating → gluing → glass assembly → fixing → cleaning → glass sealing. Each process should be carefully and carefully operated according to the operating process. Even a small negligence will cause a weak link in use, which will affect its construction quality and service life.

2. Structural adhesive

Structural adhesives are mainly used for the bonding of auto parts, and structural adhesives are mostly solvent-free two-component polyurethane adhesives. Structural polyurethane adhesives are used to join structural components such as metal, plastic, glass, wood, etc. instead of bolts, rivets or welding.

The first successful bonding of automotive parts was Goodyear's Pliogrip, a solvent-free two-component reactive adhesive that was used in 1967 for the bonding of 5MC hoods for trucks. Subsequently, companies such as General Motors and Ford successively used it for bonding on the SMC (sheet molding compound) parts of large trucks. Then it was extended to FRP (glass fiber reinforced plastic) parts.

The synthetic solvent-free structural polyurethane adhesive has the characteristics of simple use process, convenient storage and transportation, etc. It can be cured at room temperature or heat, and its adhesive layer has elasticity and high shear strength. Satisfactory results have been achieved in the application.

In order to make the structural polyurethane adhesive more competitive, researchers in various countries are continuing to work on a lot of modification work. For example, in order to further improve the heat resistance and its strength, the polyurethane adhesive is modified with epoxy resin. The polymer is then cured by crosslinking through the reaction of epoxy groups with amines. Thereby, the adhesive of polyurethane-epoxy-polyurea structure with high hardness, high shear strength and high chemical resistance is prepared. The polyurethane adhesive modified by adding nano-filler can not only reduce the cost, but also improve its crystallinity, so that its shear strength and initial tack force are greatly improved. The modified solvent-free polyurethane adhesive which is grafted or copolymerized with polyurethane and acrylate and forms an interpenetrating network with polystyrene can be used without primer. It can not only improve the curing speed and initial adhesion, but also prevent the generation of air bubbles; different types of adhesives are prepared by using polyols with different structures and polyisocyanates with different structures to adapt to the bonding of different substrates, so that the adhesive tends to be functionalized.