To provide (1) a surface treatment composition sufficiently and stably imparting a rubber surface with properties such as non-tackiness and lubricity and a surface-treatment method and (2) a method for producing a relief valve for low-pressure use free from large deviation of the working pressure from preset pressure even after leaving the valve in closed state for a long period.

The surface treatment composition contains a tetraalkoxysilane, a silane coupling agent and a solvent. The surface treatment method contains a step to apply the surface treatment composition to a surface of a rubber and a step to heat the formed coating film. The method for the production of a relief valve for low-pressure use having a valve provided with an O-ring contacting to and separating from a valve seat contains a step to apply the surface treatment composition to the O-ring and heat the coating film of the composition to perform the surface-treatment of the O-ring and a step to mount the surface-treated O-ring as a component of the valve.

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