How To Use Silane Coupling Agent
surface pretreatment
The silane coupling agent is formulated into a dilute solution with a concentration of 0.5-1%. When using, just apply a thin layer on the clean surface to be adhered, and it can be glued after drying. The solvent used is mostly water, alcohol (methanol is selected for methoxysilane, ethanol is selected for ethoxysilane), or a mixture of water and alcohol, and water without fluoride ion and cheap and non-toxic ethanol and isopropanol are suitable. In addition to aminohydrocarbyl silane, the solutions prepared by other silane coupling agents should be added with acetic acid as a hydrolysis catalyst, and the pH value should be adjusted to 3.5-5.5. Long-chain alkyl and phenyl silanes are not suitable for use in aqueous solutions due to their poor stability. The hydrolysis process of chlorosilane and ethoxysilane is accompanied by a serious condensation reaction, and it is not suitable to be used as an aqueous solution or a hydroalcoholic solution, but mostly as an alcohol solution. For silane coupling agents with poor water solubility, 0.1-0.2% (mass fraction) of non-ionic surfactants can be added first, and then water is added to process them into aqueous emulsions. [6]
Migration method
The silane coupling agent is directly added to the adhesive component, and the general addition amount is 1-5% of the base resin. After the glue is applied, the molecules of the coupling agent migrate to the bonding interface to generate the coupling effect by the diffusion of the molecules. For the adhesive that needs to be cured, it needs to be cured for a period of time after gluing, so that the coupling agent can complete the migration process, and then a better effect can be obtained.
In actual use, the coupling agent often forms a deposition layer on the surface, but what really works is only the monomolecular layer, so the amount of the coupling agent does not need to be too much.
The use methods of silane coupling agent mainly include surface pretreatment method and direct addition method. The former is to treat the surface of the filler with the diluted coupling agent, and the latter is to add the original solution of the coupling agent when the resin and the filler are premixed.
The silane coupling agent is formulated into a solution, which is conducive to the dispersion of the silane coupling agent on the surface of the material. The solvent is a solution prepared from water and alcohol. The solution is generally silane (20%), alcohol (72%), water (8%) , Alcohols are generally ethanol (p-ethoxysilane) methanol (p-methoxysilane) and isopropanol (for silanes that are not easily soluble in ethanol and methanol). Because the hydrolysis rate of silane is related to the pH value, the neutrality is the slowest and the partial Acid and partial alkali are both relatively fast, so 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 is alkaline and does not need to be adjusted. Because silane cannot be stored for a long time after being hydrolyzed, it is best to use it now, and it is best to use it up within an hour.
The following are some specific applications for users' reference:
pretreatment packing method
Put the filler into the solid mixer (high-speed solid mixer HENSHEL (Henschel) or V-type solid mixer, etc.), and spray the above silane solution directly on the filler and stir, the higher the rotation speed, the better the dispersion effect. Generally, stir for 10-30 minutes (the slower the speed, the longer the time), and the filler should be dried at 120 degrees Celsius (2 hours) after processing.
aqueous solution
(Glass fiber surface treatment agent): Glass fiber surface treatment agent often contains: film-forming agent, antistatic agent, surfactant, coupling agent, water. The amount of coupling agent is generally 0.3% to 2% of the total amount of glass fiber surface treatment agent. The 5 times aqueous solution is first adjusted to a certain value with organic acid or salt, and under full stirring, add silane until transparent, and then add For the remaining components, for insoluble silanes, isopropanol can be used as a co-dissolving aid. During the drawing process, spray the glass fiber surface treatment agent on the glass fiber and dry it to remove the solvent and water.
Bottom method
The solution of 5% to 20% of silane coupling agent is as described above, and the surface of the substrate is treated by coating, brushing, spraying, and dipping. Take out and dry at room temperature for 24 hours, preferably at 120 ° C for 15 minutes.
direct accession
Silane can also be added directly to the filler/resin mixture. When the resin and filler are mixed, the silane can be sprayed directly into the mixture. The amount of coupling agent is generally 0.1% to 2% of the amount of filler (determined according to the diameter of the filler). The silane-added resin/filler is then molded (extruded, compression molded, coated, etc.).
