The curing process of polyurethane adhesives directly affects the bonding strength, durability and final performance. The control of its curing is a key step in application. The following are the main points that need attention:
1. Strictly control environmental conditions
Humidity and temperature are the core influencing factors. Polyurethane is sensitive to moisture. The moisture in the air reacts with the isocyanate groups to produce carbon dioxide, which may cause foaming of the adhesive layer or result in defects. Therefore, the construction environment should be kept dry (the relative humidity is generally recommended to be below 70%), and the surface of the object to be bonded also needs to be dry and clean. Temperature affects the speed and degree of curing: if the temperature is too low (such as below 10℃), it will lead to slow reaction, poor initial adhesion, and incomplete curing; if the temperature is too high, it may cause the reaction to be too fast, affecting the operation or generating internal stress. Generally, the optimal curing temperature is between 15-30℃, and it needs to be maintained stably.
2. Precise Control of Ratio and Mixing
For two-component polyurethane adhesives, the proportions must be accurately measured according to the specifications provided in the product manual. Deviations in the proportions can result in incomplete curing or reduced performance. The mixing should be thorough and uniform to avoid any unreacted areas, but the stirring should not be too rapid to prevent the introduction of excessive air bubbles. The mixture should be used within the applicable period; otherwise, an increase in viscosity will affect the coating and penetration effects.
3. Ensure surface treatment and adhesive application quality
The surface of the materials to be bonded should be properly treated to remove oil stains, rust, and release agents. If necessary, grinding or chemical treatment can be carried out to enhance the wettability and adhesion. The adhesive application should be uniform, with an appropriate thickness, avoiding any gaps or excessive thickness in certain areas. For porous materials, pre-coating or increasing the amount of adhesive can be considered.
4. Control of Pressing Pressure and Time
Applying pressure helps the adhesive fully penetrate the surface, eliminate air bubbles, and form a uniform layer. The pressure should be uniform and moderate. Excessive pressure may cause excessive bleeding of the adhesive, resulting in insufficient glue, while too little pressure may lead to poor contact. The curing time must be sufficient. After the initial curing, a maintenance period (such as 24-72 hours) is often required to reach the final strength. During this period, it is necessary to avoid premature loading or moving the components.
5. Safety and Storage
Unsolidified components (especially those containing isocyanates) may be irritating to the skin and respiratory system. During operation, ventilation should be provided and protective equipment should be worn. When storing, the container must be sealed to prevent moisture and avoid exposure to high temperatures or freezing.
