The utilization of solvents in the paint industry holds greater significance compared to other industries. The drying time of paint after brushing is determined by the percentage of non- volatile components in the paint, which refers to the solvent that achieves the desired and usable concentration through its dissolving ability. The choice of solvent plays a crucial role in determining the properties of the paint. The selection of a solvent is based on various properties, including solubility power, evaporation rate, boiling point, flash point, price, color, odor, and anti-corrosion resistance.

Solubility refers to the capacity of a solvent to dissolve resins or other substances. The point at which the resin settles in the solvent is known as the dilution limit, occurring as the percentage of solvent to resin increases. Understanding the dilution limit of a solution is crucial in determining the level of compatibility between a resin and a solvent. The next factor to consider is volatility, which refers to the rate of evaporation of a solvent. This factor directly impacts the uniformity of the surface, the flow of the glaze, and the glossiness of the drying brush. The evaporation rate of a solvent is crucial for thermoplastic paints, as a solvent with a slow evaporation rate can extend the drying time, leading to compromised flow and color fading. Because there is little delay in drying the paint film, fast-volatile solvents are used more frequently than other solvents. However, when fast- volatile solvents are used alone, they not only lead to flow issues but also result in rapid evaporation. This rapid evaporation creates a significant concentration disparity between the surface and the underlying layers, causing the surface to dry out before the deeper layers. Consequently, this leads to the formation of spots. Consequently, it is advisable to employ rapid and unstable solvents as a combination.

The next variable to consider is the boiling point, which refers to the temperature at which the vapor pressure of a solvent becomes equal to the atmospheric pressure. Another important consideration is the flash point. The flash point temperature refers to the specific temperature at which a liquid or its mixture produces enough vapor to ignite and sustain a flame within a short period. There is an inverse relationship between the evaporation rate of a solvent and its flash point: as the evaporation rate increases, the flash point decreases, and vice versa. Another important consideration is toxicity. Solvents are typically toxic, and as a result, their toxic vapors can be absorbed into the bloodstream through inhalation, posing a health risk to the body. Examples of toxic solvents include methanol, benzene, and cyclohexanone. Some examples of less toxic solvents are toluene, xylene, and 402. The subsequent factor to consider is the specific weight. An appropriate solvent should possess an equivalent standard specific weight as that of the solvent in question. The specific weight can be determined using a device known as a pycnometer.

The solvents’ ability to resist corrosion and acidity is crucial. Solvents must be free from sulfur compounds that have a detrimental impact on metals and can react with pigments and resins, leading to corrosion.