Water-repellent thin film with high alkali resistance using the sol-gel method for ink jet printer head

Water-repellent thin films from si lane coupling agents have been widely used for inducing hydrophobicity on various surfaces. However. films obtained by conventional methods have poor durability against alkaline solutions. A new water-repellent thin film with high alkali resistance has been obtained for the first time by the sol-gel method using fluoroalkylinethoxysilane and 1,4-bis(trimethoxysilylethyl)benzene (BTB). The film maintained its hydrophobicity after soaking in alkaline ink with pH = 8.9 at 70degreesC for 500 h. While the film maintained alkali resistance after being heat-treated at temperatures Lip to 300degreesC, that heat-treated at 400degreesC lost its alkali resistance. Fourier transform infrared measurements of the film indicated that ethyl groups in BTB molecules burn or oxidize at 400degreesC. It is speculated that the ethyl groups in the vicinity. of siloxane bonds and the three-dimensional BTB polymer network prevent OH- ions from approaching and breaking the siloxane bonds in the film. and thus the film has high alkali resistance. We demonstrate that the new water-repellent film is applicable to the ink jet printer head.