2 декабря, 2015 
Pokraskin According to DIN EN 971-1, solvents are defined as liquids comprising one or more components that are volatile under the specified drying conditions and capable of dissolving binders purely physically without any chemical reactions.
Most resins used as binders for solventbased or high-solid coatings are solids or viscous liquids that need to be diluted to lower viscosity for easy processing into paint, ease of applicability of the paint and better film formation thereafter due to evaporation. Thus, even though solvents are not an integral part of dry coating films, they are important components of paints and coatings.
Apart from their primary role of providing lower viscosity for proper application, solvents also play a significant role in paint processing as well as in controlling final film properties. Solvents reduce the viscosity and, in most cases, the surface tension of the binder, which assists the wetting process at the pigment dispersion stage of paint manufacturing. Once the films are applied, solvents also assist in better flow and leveling, which improves appearance and gloss of coatings. In some reactive systems, solvents such as alcohols and ketones may influence the kinetics of certain crosslinking reactions and pot life (in two-component systems). In metallic paints, use of solvent combinations plays a vital role in orientation of the metal flakes, which controls the final appearance of films.
In contrast to the solvents described above, a reactive solvent is defined as a solvent that undergoes a chemical reaction with a binder during film formation and becomes an integral part of the dry
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film. These types of solvents are important due to their reduced or no emissions, making them useful in low-VOC coatings.
Solvents are frequently classified based on their relative solvency. Prime solvents (also known as true solvents or active solvents) are solvents capable, by themselves, of dissolving a resin. For example, aliphatic hydrocarbons are true solvents for long oil alkyds and esters are true solvents for nitrocellulose. Latent solvents are not true solvents for a resin, but they enhance the solvency of a true solvent. For example, alcohols are latent solvents for nitrocellulose. Diluents or extenders for solvents are volatile liquids that cannot dissolve a resin by themselves but are frequently used in combination with true solvents to balance the overall evaporation rate of a coating and/or reduce the overall cost of the coating. For example, aromatic hydrocarbons are diluents for nitrocellulose lacquers.
Thinner is the term generally used in the coating industry to describe an optimized combination of the abovementioned types of solvents, which is added to coatings just before application to reduce the viscosity of the coating in order to assist better application.
In general, solvents to be used for coatings should have the following desirable properties:
• Dissolve the binder completely
• Clear and colorless appearance
• Volatile enough to leave the film completely without leaving residue
• Inert to other ingredients of the paint
• Minimum odor or pleasant odor
• Consistent physical properties as per specifications
• Low toxicity
• Low cost
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