F A Q

We understand that the solutions of silane coupling agent ares diluted when silane coupling agents are applied. Howare the solutions made?

Silanes are usually diluted with water to a concentration of approximately 0.1 - 2.0 %. If using silanes that are not soluble in water, a combination of 0.1 - 2.0 % of acetic acid in water or water-alcohol (acetic acid, water, and alcohol together) is recommended. Acetic acid is used to control hydrolysis rates. Adjustment of the pH greatly influences the stability of silanols.

How to prepare standard diluted solutions

(1) Prepare the water solution by adding acetic acid to a final concentration of 0.1 - 2.0 %. If the silanes are more soluble, a lower concentration of acetic acid is recommended. For aminosilanes, there is no need to add acetic acid.

(2) Mix the acetic acid solution while dropping the silanes to achieve a final silane concentration of approximately 0.1 - 2.0 %. By mixing the solution rapidly while dropping the silanes slowly, gel formation can be avoided.

(3) After adding the silane, stirring should be continued for another 30~60 minutes until the solution becomes transparent, indicating that the hydrolysis of the silane is complete.

(4) Filtration should follow, if necessary. Filtration is recommended if solid impurities occur. If the silane solution is to be used continuously, a cycle of filtration with a cartridge below 0.5 µm is recommended.

(5) The stability of each Shine-Etsu silane coupling agent is given below.

The alkoxysilyl group reacts with water to yield a silanol group that is not stable and will condense rapidly to form a siloxane structure. A silanol is usually not stable in the presence of water, but it is more stable in weakly acidic solutions. Aminosilanes are an exception since the amino group helps the silane to become more stable in water solutions. The following table gives information concerning water solutions of several products and their most stable pH values.