There are various methods for modifying the surface state of a substrate through a treatment using an appropriate agent to specifically improve certain surface properties. For example, in the field of mechanics, and in particular in the field of horology, but also in the field of jewelry, epilamization of a surface of a piece or of an element is often achieved by means of an epilame agent to control and reduce the surface energy of said surface during use. More specifically, the purpose of an epilame agent is to prevent the spread of oil or lubricants over the elements of a timepiece or piece of jewelry by forming an invisible, hydrophobic and oleophobic molecular layer at the surface of the element allowing the lubricant to remain in a predetermined place on the treated surface and thereby prevent it from spreading. Keeping the lubricant in its operating area increases its durability.
Currently, most epilame agents available on the market, such as Moebius® Fixodrop® FK/BS or the 3M™ Fluorad™ range (FC-722 and others), consist of a fluoropolymer dissolved in a perfluorinated or fluorinated solvent. The epilamization method is conventionally achieved by dip coating the components to be epilamized in an epilame bath formed of a perfluorinated or fluorinated solvent loaded with epilame agent.
The most commonly used fluorinated solvents until recently were tetradecafluorohexane and 3M™ HFE-7100. However, tetradecafluorohexane has, in particular, the drawback of forming, once evaporated, a greenhouse effect gas, since it remains air-stable for 3,200 years and has a global warming potential of 7,400 CO2 equivalents.
Since the use of such solvents has been prohibited by new environmental regulations, new fluorinated solvents have been developed. However, although these new-generation fluorinated solvents (such as 3M™ HFE-7200) are less stable in air, they still have an impact on the environment. They therefore require the use of machines or other closed equipment and are likely to be affected by even more strict regulations in the future. Further, these new-generation fluorinated solvents are relatively expensive.
To replace the conventional epilamization method using toxic and expensive fluorinated solvents, EP Patent Application 1927648 proposes an epilamization method with an epilame molecule solution in a mixture of water and propanol. This epilamization method has the drawback of only being able to be used with a very limited number of epilame agents since the epilame molecules must be soluble in the water/propanol mixture. However, it is well known to those skilled in the art that the best epilame properties are obtained with fluorinated molecules which therefore have very low solubility in a water/propanol mixture.
Finally, the concentrations of epilame agent used in the conventional dip coating epilamization method are very low (typically comprised between 20 mg/L and 250 mg/L) and the fluorinated solvents used are volatile (boiling temperature lower than 100° C.). Consequently, the day-to-day industrial management of epilame baths is complex because the concentration of epilame agent in the epilame bath has to be checked by titration and a concentrated solution of epilame agent or solvent must be added according to changes in the composition of the epilame bath.