1. Surface pretreatment method
Prepare a dilute solution of 0.5-1% concentration of silane coupling agent, and apply a thin layer on the clean surface to be adhered. After drying, the adhesive can be applied. The solvents used are mostly water, alcohol (methanol for methoxysilane and ethanol for ethoxysilane), or a mixture of water and alcohol, with water free of fluoride ions and inexpensive and non-toxic ethanol and isopropanol being preferred. Except for aminoalkylsilane, solutions prepared with other silane coupling agents require the addition of acetic acid as a hydrolysis catalyst and the adjustment of pH to 3.5-5.5. Long chain alkyl and phenylsilane are not suitable for use as aqueous solutions due to their poor stability. During the hydrolysis process of chlorosilanes and ethoxysilanes, there is a serious condensation reaction, and they are not suitable for use as aqueous solutions or aqueous alcohol solutions. Instead, they are often used as alcohol solutions. For silane coupling agent with poor water solubility, 0.1~0.2% (mass fraction) of non-ionic surfactant can be added first, and then water can be added to process it into water lotion for use.
2. Migration Law
Directly add silane coupling agent to the adhesive component, usually in an amount of 1-5% of the base resin. After gluing, the coupling agent molecules migrate to the bonding interface through molecular diffusion, resulting in coupling action. For adhesives that need to be cured, they need to be left for a period of time after coating to allow the coupling agent to complete the migration process and achieve better results.
In practical use, coupling agents often form a deposition layer on the surface, but only the single molecular layer actually works, so the amount of coupling agent used does not need to be too much.
The main methods for using silane coupling agents are surface pretreatment and direct addition. The former involves treating the surface of fillers with diluted coupling agents, while the latter involves adding the original solution of coupling agents during resin and filler pre mixing.
The solution of silane coupling agent is conducive to the dispersion of silane coupling agent on the surface of materials. The solvent is a solution prepared by water and alcohol. The solution is generally silane (20%), alcohol (72%), water (8%), and alcohol is generally ethanol (para ethoxysilane), methanol (para methoxysilane), and isopropanol (for silane that is not easily soluble in ethanol or methanol). Due to the fact that the hydrolysis rate of silane is related to the pH value, neutral is the slowest, and acidic and alkaline are relatively fast. Therefore, it is generally necessary to adjust the pH value of the solution. Except for aminosilane, a small amount of acetic acid can be added to other silanes to adjust the pH value to 4—5， Aminosilane does not need to be adjusted due to its alkalinity. Due to the hydrolysis of silane, it cannot be stored for a long time and is best prepared and used immediately, preferably within one hour.
