The bonding process is an operation step that uses an adhesive to connect the adherends into a whole. The process is to first repair the surface to be adhered of the adhered workpiece to make it fit well; secondly, according to the material and strength requirements, the adhered surface is repaired. The surface is subjected to different surface treatments; then the adhesive is applied to assemble the surfaces to be adhered; finally, it is cured by physical or chemical methods to realize the adhesive connection.

The bonding process between the adhesive and the surface of the material to be bonded is a complex physical and chemical process. The bonding force of the interface attracts and connects with each other through the intermolecular force to achieve a certain bonding strength. Therefore, the bonding strength not only depends on the composition and formulation, surface structure and morphology of the adhesive, but also has a close relationship with the bonding process. For example, the surface treatment of the adherend, the coating method, the thickness of the adhesive layer, and the curing conditions , drying time and temperature, etc. Surface treatment of adherends There are various types of adherends and their surfaces. There are metal and non-metal; polar and non-polar; there are smooth or dense surfaces, and there are rough or porous surfaces; there are clean and hard surfaces, and there are stained, loose surfaces, etc. There are often rust, grease, dust, etc. on the bonding surface. These attachments hinder the infiltration of the adhesive on the surface, reduce the mutual contact between the adhesive and the adherend, and seriously affect the bonding performance. In order to obtain automotive adhesive products with high bonding strength and good durability, various bonding surfaces must be properly treated. The function of surface treatment is to change the state of the surface that is not conducive to bonding, obtain a clean, dry, rough and active surface, and ensure that the adhesive and the adherend are fully wetted and tightly combined to achieve a firm bond. .

The commonly used surface treatment methods are as follows:

一、Surface treatment of metal materials

The surface of the metal material is affected by the ambient atmosphere, and pollutants, gas layers (nitrogen, oxygen, carbon dioxide, etc.), oxide layers, work-hardening layers, etc. are adsorbed on the surface. Surface treatment of metal materials mainly includes degreasing, rust removal and activation。

（一）There are four main methods for degreasing and degreasing the surface of metal materials:。

1、Organic solvent degreasing 

Organic solvents can remove various oils on the metal surface without corroding the metal. It is easy to operate and has many applications. Commonly used degreasing solvents include steam, ketone, alcohol, toluene, trichloroethylene, carbon tetrachloride, etc. General-purpose solvent degreasing type, cotton yarn dipped in organic solvent to scrub the metal surface, but this method is suitable for single-piece production. It is low and has high toxicity to the human body. In recent years, the gas-phase solvent degreasing method has been widely used. The lower part of the closed container is placed in a low-boiling organic solvent, the workpiece is hung in the container, and the solvent is volatilized into vapor by a little heat, which condenses into droplets on the working surface and falls down, making the pollution Dissolved in solvent. Such as trichlorohexene, trifluorotrichloroethane gas phase degreasing method. The use of vapor phase degreasing method can avoid operator contact with solvent. The organic solvent degreasing method sometimes cannot completely remove the oil stains at one time, and needs to be cleaned repeatedly。

2、lye degreasing

The lye degreasing has the characteristics of non-toxic, non-flammable and economical, and it is widely used in qualified units. The principle of lye degreasing is to realize degreasing by means of saponification and emulsification. The so-called saponification refers to the reaction of oil and alkali to generate high-carbon fatty acid salts and glycerol. The emulsification is that the alkane mineral oil breaks into discontinuous oil droplets in the lye, and wraps the lye on the surface of the oil droplets, reducing the tension of the oil-water interface, reducing the affinity of the oil for work, and allowing the oil droplets to enter the solution. , to achieve the purpose of degreasing. After using lye to treat the object, it must be fully washed with water many times to remove the residual lye on the surface of the workpiece, otherwise it will greatly affect the bonding strength. In recent years, some new surfactant-based degreasing and cleaning agents have appeared, such as 801, 802, 310, etc., which have the advantages of strong decontamination, easy to use, and no waste liquid pollution.。

3、Electrolytic degreasing 

Electrolytic degreasing is an effective means to remove oil stains. The principle of degreasing is that in alkaline electrolyte, the surface tension between oil and lye is reduced, which promotes cracks in the oil film. The surface tension between the two is reduced, and the contact area between the two is increased, forcing the oil stains adsorbed on the metal surface to become fine oil droplets. Under the action of the current, hydrogen bubbles or oxygen bubbles are generated on the surface of the electrode, which stay on the small oil droplets. With the progress of electrolysis, the bubbles gradually become larger. When sufficient buoyancy is reached, the bubbles carry the oil droplets away from the metal surface. Reached the degreasing day. Compared with lye degreasing, electrolytic degreasing has higher efficiency and better quality。

4、Ultrasonic degreasing

Ultrasonic degreasing is to put the workpiece to be degreasing in the ultrasonic cleaning tank, put a solvent or a solution containing surfactant in the tank, and then start the high-frequency generator, when the ultrasonic frequency reaches 20 ~ 5000Hz, the generated energy makes The solution in the tank is turned over, and the working surface is washed, so that the oil pollution is impacted. This method is generally only suitable for degreasing of small precision parts. When ultrasonic degreasing, the appropriate solvent can be selected according to the type of degreasing work。

（二）, Derusting the surface of metal materials 

The rust layer and contamination on the surface of metal materials can be removed by mechanical or chemical treatment. Mechanical rust removal is one of the commonly used surface treatment methods in the industry. It can directly remove the dirt on the surface, and can also obtain a certain surface roughness and increase the bonding strength, which is very beneficial for bonding and sealing. The specific methods include manual removal. Rust, power tool rust removal, sandblasting and rust removal. Chemical rust removal is to chemically corrode the metal in an active solution, which can not only activate or passivate the surface, but also form a surface oxide layer with good cohesive strength on the metal surface, which is very beneficial for forming a strong bond. There are two types of chemical rust removal: chemical etching and electrochemical etching.。

（三）Activation of metal surfaces

For general metal materials, they can be bonded after degreasing, degreasing, and rust removal. If you want to further improve the bonding strength of metal materials and reduce the dispersion of bonding strength, the surface can be activated to further remove the inert substances on the metal surface, so that the surface is in a state of high surface energy, which is conducive to the lubrication of the adhesive. wet. In addition to treating metal surfaces by activation, phosphating is often used in metal surface treatment. Phosphating refers to the process in which steel is treated in a phosphating solution to deposit a layer of water-insoluble crystalline phosphate conversion film on the surface. The steel treated with phosphating has good corrosion resistance, and the adhesion between the paint film and the steel parts is increased, which reduces the possibility that the adhesive is corroded and the paint film is separated from the steel plate during the bonding process, and improves the bonding strength.。

（四）Metal surface primer activation

Apply a primer to the treated metal surface to improve adhesion. Primer coating can improve the bonding performance, protect the metal surface cleanliness, prolong the validity period of the treated surface, and improve the adhesion performance of the surface to be adhered. The most typical method is to coat the coupling agent, so that a good chemical bond is formed between the coupling agent and the material to be adhered, and the bonding strength and the ability of the joint to resist external influences are improved. Surface treatment of non-metallic materials Non-metallic materials include rubber, plastic, glass, ceramics, wood, etc., especially polymer materials, such as polytetrafluoroethylene, polypropylene, polyethylene, etc., the surface energy is low, and it is difficult to be completely wetted , must be surface treated before bonding。