The bonding process between the adhesive and the surface of the bonded material is a complex physical and chemical process. The bonding force of the interface attracts and connects each other through the intermolecular force, and reaches a certain bonding strength. Therefore, the bonding strength not only depends on the composition and formula of the adhesive, surface structure and morphology, but also has a close relationship with the bonding process. For example, the surface treatment of the adhesive, the coating method, the thickness of the adhesive layer, the curing conditions, the drying time and temperature. Surface treatment of the bonded material The bonded material and its surface are varied.

      Bonding process is the use of adhesive to connect the adhesive into a whole operation step, the process is first to repair the surface of the workpiece to be bonded to make it fit well; Secondly, according to the requirements of material and strength, the sticky surface is treated differently. Then the adhesive is coated and the adhesive surface is assembled together; Finally, it is cured by physical or chemical methods to realize adhesive connection.

    The bonding process between the adhesive and the surface of the bonded material is a complex physical and chemical process. The bonding force of the interface attracts and connects each other through the intermolecular force, and reaches a certain bonding strength. Therefore, the bonding strength not only depends on the composition and formula of the adhesive, surface structure and morphology, but also has a close fire relationship with the bonding process. For example, the surface treatment of the adhesive, the coating method, the thickness of the adhesive layer, the curing conditions, the drying time and temperature. Surface treatment of the bonded material The bonded material and its surface are varied. Having metal or non-metal; Polar or non-polar; There are smooth or dense surfaces, but also rough or porous surfaces; There are clean, hard surfaces, but also stained, loose surfaces. The adhesive surface is often rusted, greasy, dust, etc. These attachments prevent the adhesive from infiltrating the surface, reduce the contact between the adhesive and the adhesive, and seriously affect the bonding performance. In order to obtain automobile adhesive products with high bonding strength and good durability, it is necessary to treat various bonding surfaces appropriately. The role of surface treatment is to change the state of the surface that is not conducive to bonding, to obtain a clean, dry, rough, active table, and to ensure that the adhesive and the adhesive are fully wetted and closely combined to achieve a firm bonding.

      Commonly used surface treatment methods are as follows:
      1. Surface treatment of metal materials 
      The surface of the metal material is affected by the environmental atmosphere, and there are pollutants, gas layers (nitrogen, oxygen, carbon dioxide, etc.), oxide layers, work hardening layers, etc., adsorbed on the surface. The surface treatment of metal materials mainly includes oil removal, rust removal and activation.
   (1) There are four main methods for removing oil from the surface of metal materials
      1, organic solvent oil removal 
      Organic solvents can be a variety of oil on the surface of the metal and do not corrode the metal, easy to operate, more applications, commonly used oil removal solvents are steam, ketone,. Alcohol, toluene, trichloroethylene, carbon tetrachloride, etc. The common solvent degreasing type, cotton yarn dipped in organic solvent scrub metal surface, but this method is suitable for single piece production. Low, more toxic to human body. In recent years, the gas phase solvent degreasing method has been widely used. Close the lower part of the container into the low boiling point of the organic solvent, the workpiece is hung in the container, the slight heat makes the solvent volatilize into vapor, condenses into liquid drops on the working surface and falls, so that the pollution is dissolved in the solvent. Such as trichlorohexene, trifluorotrichloroethane gas phase oil removal method. The gas phase degreasing method can avoid contact between the operator and the solvent. Organic solvent oil removal method, sometimes can not be completely removed once, need to be cleaned repeatedly.

      2, lye oil removal
      Lye oil removal has the characteristics of non-toxic, non-combustible and economic, and it is applied more in the units with conditions. The principle of lye oil removal is to achieve oil removal by saponification and emulsification. The so-called saponification refers to the reaction of oil and alkali to produce high-carbon fatty acid salts and glycerol. The emulsification effect is that the alkane mineral oil breaks into discontinuous oil beads in the lye, and the lye is wrapped on the surface of the oil beads, which reduces the tension of the oil and water interface, reduces the affinity of the oil to the work, and makes the oil droplets enter the solution to achieve the purpose of oil removal. After the use of lye to handle the vermicular substance, it is necessary to wash it fully with water several times to remove the residual lye on the surface of the workpiece, otherwise the bonding strength will be greatly affected. In recent years, some new surfactants have appeared, which have the advantages of strong decontamination power, simple use and no waste liquid pollution.

      3. Electric disoil 
      Electric oil removal is an effective means to remove oil, the principle of oil removal is in the alkaline electrolyte, due to the surface tension between the oil and lye is reduced, to promote the oil film cracks, while the electrode polarization between the metal and lye surface tension is reduced, the contact area between the two increases, forcing the metal surface and the adsorption of oil into small oil droplets. Under the action of the current, the electrode surface produces hydrogen bubbles or oxygen bubbles, which are retained on the small oil beads. With the progress of electrolysis, the bubbles gradually grow larger. When sufficient buoyancy is reached, the bubbles carry the oil beads out of the metal table and achieve the degreasing day. Compared with lye deoiling, electrolysis method has higher efficiency and better quality.

      4, ultrasonic oil removal 
      Ultrasonic degreasing is to put the workpiece to be degreased in the ultrasonic cleaning tank, where there is a solvent or a solution containing surfactants, and then start the high-frequency generator, when the ultrasonic frequency reaches 20 ~ 5000Hz, the energy generated makes the solution in the tank flip, and washes the working surface, so that the oil is impacted down. This method is generally only suitable for the removal of small precision parts. When ultrasonic oil removal, the appropriate solvent can be selected according to the type of oil removal work.