The film forming process of the solvent type film forming agent is an important technical link in the leather finishing. In this paper, we share with you what the film forming process of the solvent type film forming agent in the leather finishing.
The basic principle of leather finishing is concentrated on film forming. The film formation process is usually discussed in terms of solvent type and water solubility and film forming process of emulsion type film-forming agent. In the film forming process, the formation of the film refers to the process of transforming the liquid forming agent into a solid state, which includes two parallel and interrelated processes, evaporation of the volatile components in the liquid and the formation of the film structure.
The formation of film is the result of volatilization of volatile components in solvent based film forming agent. Volatile components include solvents and diluents, the most important property of which is the evaporation rate. The rate of evaporation is related to the vapor pressure of the volatile components. The greater the vapor pressure, the faster the evaporation. The evaporation rate can also be judged by the boiling point of the liquid.
The evaporation of solvents from film forming agents can be divided into three stages.
The first phase: when the membrane is coated on the surface, a large number of diluents and solvents in the liquid film begin to evaporate, and their evaporation process is the same as the pure solvent evaporation on the free surface, but this process is very short.
In the second stage, a thin film is formed on the surface of the film forming agent, first of the adhesive gel and then into the gel, which increases with the thinning of the liquid film.
The third stage: the solvent with the closest combination with the film forming agent starts to evaporate. Although the volatile part evaporates into the air after film formation, it does not remain in the film, but it has a great influence on the film formation process. If the solvent first evaporates and the diluent evaporates, the nitrocellulose or resin will precipitate. In addition, if the evaporation of volatile components is too fast and the temperature of the film surface decreases rapidly, the moisture in the space around the membrane will be condensed on the surface of the film to make the film white. Therefore, attention must be paid to the selection of solvents and diluents.