Surface pretreatment method
The silane coupling agent is formulated into a dilute solution having a concentration of 0.5 to 1%. When used, it is only necessary to apply a thin layer on the cleaned surface to be adhered, and after drying, the glue can be applied. Most of the solvents used are water, alcohol (methanol for methoxysilane, ethanol for ethoxysilane), or a mixture of hydroalcohol, and water with no fluoride ion and inexpensive non-toxic ethanol or isopropanol. In addition to the aminoalkyl silane, solutions prepared from other silane coupling agents are required to be added with acetic acid as a hydrolysis catalyst and the pH is adjusted to 3.5 to 5.5. Long-chain alkyl groups and phenyl silanes are not suitable for use as aqueous solutions because of their poor stability. Chlorosilane and ethoxysilane are accompanied by a severe condensation reaction during hydrolysis, and should not be used as an aqueous solution or a hydroalcoholic solution, and used as an alcohol solution. The poorly water-solublesilane coupling agentmay be added with 0.1 to 0.2% by mass of a nonionic surfactant, and then added with water to form an aqueous emulsion.
The silane coupling agent
is directly added to the adhesive component, and is usually added in an amount of from 1 to 5% by weight based on the amount of the base resin. After the glue is applied, depending on the diffusion of the molecules, the coupling agent molecules migrate to the bonding interface to produce a coupling effect. For the adhesive that needs to be cured, it needs to be placed for a period of time after the glue is applied to cure, so that the coupling agent can complete the migration process, and good results can be obtained.
In practical use, the coupling agent often forms a deposited layer on the surface, but only the monolayer is really effective, so the coupling agent does not have to be used in an excessive amount.
The method of using the silane coupling agent mainly includes a surface pretreatment method and a direct addition method. The former is to treat the surface of the filler with a diluted coupling agent, and the latter is a stock solution to which a coupling agent is added when the resin and the filler are premixed.
The silane coupling agent is formulated into a solution to facilitate dispersion of the silane coupling agent on the surface of the material. The solvent is a solution prepared from water and an alcohol. The solution is generally silane (20%), alcohol (72%), water (8%); the alcohol is generally ethanol (p-ethoxysilane), methanol (p-methoxysilane) and isopropyl alcohol (for silanes that are not easily soluble in ethanol or methanol). Because the silane hydrolysis rate is related to the pH value, the neutrality is the slowest, and the acid and alkali are faster. Therefore, it is generally necessary to adjust the pH of the solution. In addition to the aminosilane, other silanes can be added with a small amount of acetic acid to adjust the pH to 4-5, while the aminosilane is not need to be adjusted becauseof its alkalinity. After silane hydrolysis, it can not be stored for a long time. It is best to use it now and it is best to use it within one hour.