Лако-красочные материалы — производство

In the early phase of coating technology, due to the small number of binders, empirical selection of solvents had been adopted with the general rule of like dissolves like. But after around 1930, when a more diverse variety of synthetic binders was introduced, selection of solvents based on this rule became more difficult. As a result, more scientific approaches were developed to understand resin dis­solution, resin processing and selection of solvents for optimum performance.

A dry resin is a polymeric mass of macromolecular chains entangled and held together by secondary intermolecular attraction forces between adjacent polymeric chains. The dissolution of a polymer or a resin in a solvent is governed by the magnitude of the inter­molecular forces that exist between the molecules of the polymer and the molecules of the solvent. If polymer-polymer interactions are stronger than polymer-solvent interactions, no dissolution will occur. However, if polymer-solvent interactions are stronger, solvent molecules will tend to displace polymer chains away from each other. As the process continues, additional solvent molecules pene­trate between the polymer chains, forcing them further apart. As a result, the solvated polymer chains get disentangled into individual chains. This process is referred to as dissolution of polymer in a solvent. The forces of interaction operating between the polymer chains are of the following types.

London dispersion forces, which arise from mutual induction of atomic dipoles due to the electromagnetic field between the nucleus and electrons of the atom, leading to attraction between molecules. In the case of non-polar molecules, these are the only intermolecular forces that exist.

Dipole-dipole forces, which are the forces of attraction between molecules with a finite, permanent overall dipole moment.

Dipole-induced dipole forces, which arise from the interaction between a permanent dipole and another dipole induced by its pro­ximity to the permanent dipole.

Hydrogen bonding forces, which arise by attraction between an active hydrogen atom and electron deficient sites. Such forces can be intermolecular or intramolecular. For example, molecules having hydroxyl or amino groups act as hydrogen donors and functional groups such as esters and ketones act as hydrogen acceptors.