Solvent and thinner are two words we hear a lot, but sometimes it feels like there is no difference.

1、The basic concept of solvents and diluents solvents and diluents are chemicals that can reduce the viscosity of the resin system, make the resin and other components better mixed, or make the adhesive better applied to the surface of the substrate. Compared with polymer substances, solvents and diluents are small fraction substances, which are chemically and physically compatible with resins, curing agents, etc. So what is the difference between the two? The difference lies in the vapor pressure of both. There is also a view that solvents can dissolve the main resin and additives, while the role of diluents is mainly to reduce the viscosity of the coating system. The vapor pressure of solvents is relatively high and will be evaporated under specific environmental conditions. Some solvents can evaporate quickly at room temperature and pressure, while others may require high temperature or below room temperature and pressure to evaporate. Diluents have a very low vapor pressure and generally do not evaporate at room temperature. The main function of adding diluents to the formulation system is to reduce viscosity, improve the mixing of resin and filler, increase the amount of filler added, or improve the application properties.

2、Solvents and thinners in the coating system selection skills and principles in the coating system formulation generally need solvents with different vapor pressure, dissolution strength and dispersion ability. Let’s understand the role of solvent first. The role of solvents is to temporarily reduce the viscosity of the epoxy system, so that the resin molecules in the formulation have better mobility and fluidity. The use of solvents is mainly considered for one or more of the following reasons.

• 1) Helps dispersion, mixing and wetting of resin system during formulation making.
• (2) Reduce the viscosity of the adhesive system, so that the various components are easy to mix, as well as the use of the stage of better dispersion.
• 3) Liquidizing the solid resin or curing agent so that it can be used on the support carrier or dried to form a film on the substrate.

So when we choose a solvent, we need to take into account its solubility for that resin, as well as the viscosity, drying time and wetting effect required by the final product. All these properties affect the application performance and the bonding effect of the coating system. Usually more than one component needs to be dissolved or diluted (e.g. resin, curing agent, polymer additives, pigments, powders, etc.). Therefore, it is usually necessary to mix different solvents to achieve the required solubility or to meet certain process conditions (e.g. drying time, surface film formation, etc.). Usually, the solvents used are usually organic, and the basic rules for choosing solvents are: polar resins require polar solvents, and non-polar resins require non-polar solvents. Solvent-based resin products usually have a solids content of 10-50% and a viscosity that varies between 1000-30,000 cps depending on the specific application. The role of the solvent in a coating system system is generally to reduce the viscosity of the system to meet the process conditions of the application. When the coating is applied to the substrate surface, the solvent will evaporate before the curing reaction. Otherwise, air bubbles or vapor sacs will be generated between the bonding surfaces, resulting in reduced adhesion between the resin and the substrate. The premise of the solvent used in the formulation of the coating system is that it must not cause corrosion or other undesirable effects on the substrate being worked on. Plastics, elastomers, polymer foams, etc. are particularly sensitive to certain solvents in the coating system. Therefore, before making a formulation, it is necessary to test whether the solvent used will cause corrosion, degradation and other undesirable effects on the substrate.

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