& nbsp; & nbsp; The bonding process is the operation step of using adhesive to connect the object to be bonded into a whole. The process is to first repair the surface of the workpiece to be bonded to make it fit well; Secondly, different surface treatments should be applied to the adhered surface according to the requirements of material and strength; Then apply adhesive and assemble the adhered surface together; Finally, the adhesive connection is achieved by curing through physical or chemical methods< br />
  & nbsp; & nbsp; The bonding process between adhesive and the surface of the adhered material is a complex physical and chemical process, which generates interfacial attraction and connection through intermolecular forces to achieve 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, surface treatment of the adhesive, coating method, adhesive layer thickness, curing conditions, drying time and temperature, etc. The surface treatment of the adhered material and its surface is diverse. There are both metallic and non-metallic; Polar and non-polar; There are smooth or dense surfaces, as well as rough or porous surfaces; There are clean and hard surfaces, as well as dirty and loose surfaces. The adhesive surface often has rust, grease, dust, etc. These attachments hinder the infiltration of the adhesive onto the surface, reduce the mutual contact between the adhesive and the adhered object, and seriously affect the adhesive performance. In order to obtain automotive adhesive products with high bonding strength and good durability, it is necessary to perform appropriate treatment on various bonding surfaces. The function of surface treatment is to change the unfavorable bonding state of its surface, obtain a clean, dry, rough, and active surface, ensure that the adhesive is fully wetted and tightly bonded with the object to be bonded, and achieve a firm bonding.
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  & nbsp; & nbsp; There are several commonly used surface treatment methods, including:< br />
  & nbsp; & nbsp; 1、 Surface treatment of metal materials< br />
  & nbsp; & nbsp; The surface of metal materials is affected by the environmental atmosphere, and pollutants, gas layers (nitrogen, oxygen, carbon dioxide, etc.), oxide layers, work hardening layers, etc. are adsorbed on the surface. The surface treatment of metal materials mainly includes oil removal, rust removal, and activation< br />
  & nbsp; （1） There are four main methods for removing oil from the surface of metal materials:
  & nbsp; & nbsp; 1. Organic solvent degreasing< br />
  & nbsp; & nbsp; Organic solvents can remove various oils from metal surfaces without corroding the metal. They are easy to operate and widely used. Common oil removal solvents include gasoline, ketones, etc Alcohol, toluene, trichloroethylene, carbon tetrachloride, etc. The universal solvent degreasing type and cotton yarn dipped in organic solvents are used to scrub metal surfaces, but this method is suitable for single piece production Low, highly toxic to the human body. In recent years, gas-phase solvent oil removal methods have been widely usedPlace a low boiling organic solvent at the bottom of the closed container, hang the workpiece in the container, and slightly heat it to evaporate the solvent into vapor, which condenses into droplets on the working surface and falls down, dissolving the dirt in the solvent. Such as trichlorohexene and trifluorotrichloroethane gas-phase oil removal method. The use of gas-phase oil removal method can prevent operators from coming into contact with solvents. The organic solvent degreasing method sometimes cannot completely remove oil stains in one go and requires repeated cleaning< br />
  & nbsp; & nbsp; 2. Alkali based degreasing

  & nbsp; & nbsp; Alkali based oil removal has the characteristics of non toxicity, non flammability, and economy, and is widely used in units with conditions. The principle of alkaline oil removal is to use saponification and emulsification to achieve oil removal. The so-called saponification refers to the reaction between oil and alkali to produce high carbon fatty acid salts and glycerol. Emulsification is the process of breaking alkane mineral oil into discontinuous oil droplets in alkaline solution, and wrapping the alkaline solution around the surface of the oil droplets, reducing the tension at the interface between oil and water, decreasing the affinity of oil for work, and allowing oil droplets to enter the solution, achieving the purpose of oil removal. After treating the workpiece with alkaline solution, it is necessary to wash it thoroughly with water multiple times to remove the residual alkaline solution on the surface of the workpiece, otherwise it will greatly affect the bonding strength. In recent years, some new types of surfactant based oil removal and cleaning agents have emerged, such as 801, 802, 310, etc., which have the advantages of strong cleaning power, easy use, and no waste liquid pollution< br />
  & nbsp; & nbsp; 3. Electrolytic degreasing< br />
  & nbsp; & nbsp; Electrolytic degreasing is an effective method for removing oil stains. Its degreasing principle is that in alkaline electrolytes, the surface tension between oil and alkali solution decreases, causing cracks in the oil film. At the same time, electrode polarization reduces the surface tension between metal and alkali solution, increasing the contact area between the two and forcing the oil stains adsorbed on the metal surface to become small oil droplets. Under the action of current, hydrogen or oxygen bubbles are generated on the surface of the electrode, which remain on the small oil droplets. As electrolysis progresses, the bubbles gradually grow larger. When sufficient buoyancy is reached, the bubbles carry the oil droplets away from the metal surface and reach the oil removal day. Compared with alkaline oil removal, electrolytic oil removal has higher efficiency and better quality< br />
  & nbsp; & nbsp; 4. Ultrasonic oil removal< br />
  & nbsp; & nbsp; Ultrasonic degreasing is the process of placing the workpiece to be degreased into an ultrasonic cleaning tank. The tank is filled with a solvent or a solution containing surfactants, and then a high-frequency generator is activated. When the ultrasonic frequency reaches 20-5000Hz, the energy generated causes the solution in the tank to flip and flush the working surface, causing oil stains and other contaminants to be removed. This method is generally only suitable for degreasing small precision parts. When using ultrasonic oil removal, suitable solvents can be selected based on the type of oil to be removed.
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  & nbsp; （2） Rust removal on the surface of metal materials< br />
The rust layer and pollutants on the surface of metal materials can be removed by mechanical or chemical treatment methods. Mechanical rust removal is one of the commonly used surface treatment methods in industry, which can directly remove surface dirt and obtain a certain surface roughness to increase bonding strength, which is very beneficial for bonding and sealing. Specific methods include manual rust removal, electric tool rust removal, and sandblasting rust removal. Chemical rust removal is the chemical corrosion treatment of metals in an active solution, which not only activates or passivates the surface, but also forms a surface oxide layer with good cohesive strength on the metal surface, which is very beneficial for forming a strong bond. Chemical rust removal has two types: chemical etching and electrochemical etching< br />
  & nbsp; （3） Activation treatment of metal surfaces

After degreasing, oil removal, and rust removal, general metal materials can be bonded. If you want to further improve the bonding strength of metal materials and reduce the dispersion of bonding strength, you can activate the surface to further remove inert substances from the metal surface, making the surface in a high surface energy state, which is conducive to the wetting of the adhesive. In addition to activating metal surfaces, phosphating is often used in metal surface treatment. Phosphating refers to the process of treating steel in a phosphating solution and depositing a water-insoluble crystalline phosphate conversion film on the surface. Steel treated with phosphating has good corrosion resistance, increased adhesion between the paint film and steel parts, reduced the possibility of adhesive corrosion and detachment of the paint film from the steel plate during the bonding process, and improved the bonding strength< br />
  & nbsp; （4） Activation of metal surface coating with primer< br />
Applying a layer of primer on the treated metal surface can improve the bonding performance. Applying primer can improve adhesion performance, protect metal surfaces from cleaning, extend the effective period of surface treatment, and improve the adhesion performance of the bonded surface. The most typical method is to apply a coupling agent, which forms a good chemical bond between the coupling agent and the bonded material, thereby improving the bonding strength and the ability of the joint to resist external influences. Surface treatment of non-metallic materials, including rubber, plastic, glass, ceramics, wood, etc., especially polymer materials such as polytetrafluoroethylene, polypropylene, polyethylene, etc., have low surface energy and are difficult to fully wet. They must be surface treated before bonding.
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  & nbsp; & nbsp; 2,、 There are several surface treatments for non-metallic materials, including:< br />
  & nbsp; & nbsp; 1. Mechanical processing< br />
  & nbsp; & nbsp; Similar to the surface treatment methods for metal materials, non-metallic material surface treatment is usually carried out by sanding with sandpaper to remove surface oil stains, release agents, plasticizers, etc., before applying adhesive for bonding< br />
  & nbsp; & nbsp; 2. Physical processing

  & nbsp; & nbsp; Physical TreatmentLaw is the use of physical means such as electric fields and flames to cut; Surface treatment of adhesive materials, mainly used for non-polar polymer materials. The equipment cost is high and the processing time is long, but the effect is relatively good< br />
  & nbsp; & nbsp; 3. Chemical treatment

  & nbsp; & nbsp; The chemical treatment of non-metallic materials involves using acids, strong oxidizing agents, etc. to remove all oil and impurities from their surfaces, or to oxidize non-polar surfaces into a layer of carbon containing polar substances to enhance the bonding effect< br />
  & nbsp; & nbsp; 4. Radiation grafting treatment

  & nbsp; & nbsp; For non-polar polymers, in order to increase surface polarity and facilitate adhesive wetting, polar monomers such as polymethyl methacrylate (PM&MA), polyacrylate (PA), and vinyl acetate (V) can be usedAfter being irradiated with 00Co, the surface energy is increased. Non polar materials such as polyethylene, polypropylene, and fluoroplastics can be treated using this method. It is best to immediately bond the surface of the object after surface treatment, and the storage time should not be too long, because the treated surface has an expiration date, which is related to the type of material and the treatment method. The coating methods for adhesives include brush coating, dip coating, spray coating, and scraping coating. Different coating methods can be selected based on the purpose of the adhesive, the viscosity of the adhesive, and the properties of the adhered material. The adhesive layer should be uniform and try to avoid air accumulation in the adhesive layer after bonding. Thermosetting adhesives that do not contain solvents should be bonded immediately after coating to avoid prolonged exposure to absorb moisture from the air or volatilization of the curing agent. When using solvent based adhesive bonding, the drying time after coating can be longer to allow the solvent to fully evaporate. If there is too much solvent remaining in the adhesive layer, it will reduce the strength of the adhesive. Most adhesives that solidify by solvent evaporation will lose their elasticity if they are excessively dried after coating. Therefore, bonding should be carried out before the adhesive layer loses its adhesiveness. In some cases, the adhesive only has good adhesion to one side of the object being bonded, while its adhesion to the other side is poor. In this case, a layer of base adhesive can be applied to the difficult to bond surface, and then the base adhesive can be bonded to the other bonding surface with adhesive.