As indicated, alkyd resins are polyester-based materials that are normally modified with oil or fatty acids. These products may be further modified with a variety of other chemical materials. Various polybasic acids, polyhydric alcohols, oils, fatty acids and modifying agents may be combined to produce alkyds with specifically designed properties. The precise combination of the ingredients used, together with the careful control of the reaction, influences the final properties of the alkyd produced. For this reason, many alkyds are available to the coating formulator. In considering the applications of alkyd resins, it is convenient to take them in order of decreasing oil length.
Classification of Alkyd Resins for Paints
The alkyd-based paints can be categorized on the volume percentage of oil which they contain:
The low concentration of oil paints (30-40%) are characterized by low drying times and are used especially in the production of paints for metal surfaces (for example in
the automotive industry) or in the production of plasticizer agents for the protection of external building structures.
The medium oil content paints (45-55%) are the most versatile and they are widely used in the production of enamels both applicable by brush and airbrush.
The paints with long (55-70%) and very long (more than 70% of the total volume) oil content are characterized by a longer drying times compared to the previous categories, but are more resistant to aging and weathering. This type of paints is used mainly in the construction industry, in particular in the production of exterior paints and enamels, and in the production of products for the treatment of surfaces exposed to particularly arduous conditions, for example ships or boats of various materials.