Solvent is an important part of solvent-based coatings. It is not only used to dissolve resins and reduce viscosity to improve manufacturing and processing performance, but also affects the construction of coatings and the appearance of coating films.
Solvents are used to dissolve binders, which are helpful for production and construction. They are volatile components of coatings, which evaporate during construction and drying of the paint film. In order to obtain satisfactory results, mixed solvents are often used in actual production.
In the manufacture of coatings, two basic properties should be considered in choosing a suitable solvent, namely, solvency and volatilization speed. Solvency refers to the ability to dissolve the coating with a solvent and reduce the viscosity to achieve the application purpose.
The solvent's ability to dissolve the binder can be based on empirical rules:
A high molecular compound can be dissolved in a low molecular solvent similar to its structure.
Liquids with equal or similar cohesive energy densities can dissolve each other well.
Solvents can be divided into main solvents (active solvents), auxiliary solvents and thinners according to their functions in coatings .
The primary (reactive) solvent dissolves the resin to make a resin solution and is used as the varnish for the paint. Many synthetic resins are solid, including most alkyds, some epoxies, chlorinated rubber resins, and vinyls.
Co-solvents are usually used together with the main solvent to make the coating easy to apply and control the evaporation rate
rate and improve the quality of the final coating film.
There are many solvents that cannot dissolve the coating resin alone, but they can be mixed with a good solvent to obtain the same or greater solvency as the good solvent. This type of solvent is called a co-solvent, also known as a latent solvent. For example, alcohol solvents alone cannot dissolve nitrocellulose, but they can be mixed with ketones and ester solvents in a certain proportion to obtain greater solubility. Therefore, alcohol solvents are co-solvents for nitrocellulose.
Thinner is mainly used to dilute the ready-made paint and reduce the viscosity of the paint to facilitate construction. It is a mixed solvent composed of various solvents. The selection principle of the diluent is that it has a good dissolving , can volatilize from the paint film as the paint film dries, has no non-volatile residual substances, and is easy to mix with the solvent. At the same time, the toxicity of the diluent, factors such as flammability.
