and multiplicity make a definition almost impossible. Resins, together with drying oils, comprise the
bulk of film-forming materials, or binders, in the surface-coating field. Natural resins, such as resin and
shellac, are extracts from trees and insects. Synthetic resins, such as alkyds, alkyd modifiers (vinyls,
phenolics, silicones, epoxies), acrylics, and polyurethanes, are manufactured from basic organic
material, such as petroleum, alcohol, coal tar, and vegetable oils.
(a) Alkyds. Alkyds are the backbone of modern paint in a great many combinations.
The alkyds are characterized by toughness, flexibility, and durability Use them in exterior and interior
coatings for utility and decorative purposes. However, they do not have good chemical resistance.
(b) Alkyd modifiers. Other resins (modifiers) are combined with alkyd resins to improve
its properties. Examples of alkyd modifiers are vinyls, phenolics, silicones, and epoxies.
Vinyls. Vinyls are used where construction materials, metal, and wood must be
protected from high humidity or an acid-caustic environment.
Phenolics. Phenolics appear in varnishes and enamels that require extra hardness
Silicones. Silicones appear primarily in heat-resistant coatings. They are not
particularly hard-surfaced and may craze. They are usually baked.
Epoxies. Epoxies have outstanding adhesion and chemical resistance. In
combination with other resins, they appear as baking enamels. Air-drying types
are frequently used with converting agents just prior to application to set up films
of improved characteristics.
(c) Acrylics. Acrylics have outstanding light resistance and weather durability, and they
have moderate chemical resistance. Used with nitrocellulose as a hardener, they have better drying
properties and increased hardness. Styrene acrylic and latex emulsions are some examples of acrylics.
(d) Polyurethanes. Polyurethane coatings are characterized by a very high gloss, superior
toughness and weather durability, and good chemical resistance. They are also converted or catalyzed in
c. Varnishes. Varnishes contain oil, resins, thinners, and driers. They are produced by
combining oils and resins in definite proportions, then adding thinners and driers to the mixture. The
various types of resins, oils, and other available components make it possible to produce varnishes
adaptable to many uses. You may use varnishes as clear coatings or as vehicles for pigmented paints.
2-7. Types of Protective-Coating Materials. You must determine the best type of protective
coatings for your use. There are many factors for you to consider, such as the condition of the surface,
the method of application, curing conditions, the service expected