What are Alkyds?

Heather Phillips

Alkyds are polyester resins made from the combination of a certain kind of fatty acid, known as dicarboxilic acid, and polyol, a kind of alcohol. They are liquids and are used primarily as one of the core ingredients in many paints, varnishes, and enamel finishes. An alkyd resin base acts as a binder in these coatings, holding other ingredients together and giving them the ability to bond to many surfaces.

Alkyds are frequently used as paint binders.
Alkyds are frequently used as paint binders.

Another use for alkyds occurs in metal casting. Often in this industry, they are used to create molds. When utilized for mold-making, an alkyd resin is typically combined with a metallic dryer and a chemical, in the form of a polymeric isocyanate, to enhance drying time. In this setting, the alkyd binds sand-based molds together, drying with no toxic fumes.

When alkyds are used in paints, they give the them certain qualities that are different from water-soluble latex paints.
When alkyds are used in paints, they give the them certain qualities that are different from water-soluble latex paints.

Alkyds are also often employed widely in manufacturing electrical products. They tend to make an excellent encapsulation material for capacitors and resistors. In addition, they can be used in circuit breaker insulation and in switches. This is due to the fact that they are very heat-resistant and do not readily conduct electricity.

Alkyd-based paints are sometimes not recommended for use on masonry, concrete or galvanized metals.
Alkyd-based paints are sometimes not recommended for use on masonry, concrete or galvanized metals.

When alkyds are used in paints, they give the them certain qualities that are different from water-soluble latex paints. Generally, since alkyd products are not water-based, they bond well to wood without raising its grain. They also work well over latex paints to cover stains or discoloration. In addition, they can be used on steel and other metals that corrode in the presence of oxygen, inhibiting rust.

A further benefit of alkyds as paint binders is that they can give a thicker consistency. This results in a brush or roller picking up more of the paint. The thicker consistency, however, does not clump, but spreads evenly and smoothly because of the binder’s characteristics.

There are applications in which alkyd paint is not desirable. A few such instances are in the painting of galvanized steel, concrete, and masonry. Each of these surfaces has certain chemicals that react with alkyds and saponify, or form soap. This causes peeling and damage to the underlying material. Alkyd paint also tends to raise the nap on drywall, and is not recommended for use on it, unless the drywall has first been primed with a latex paint.

Fine artists, who often use oil paints in their work, sometimes also choose to use alkyd paints. This is generally because these dry quicker than traditional oils, and all the colors have similar drying times. A finished painting using alkyds can be varnished much faster than one using oils. Another benefit to the artist is that alkyds and oils can be combined on the same project with no detrimental effects.

Fine artists, who often use oil paints in their work, sometimes also choose to use alkyd paints.
Fine artists, who often use oil paints in their work, sometimes also choose to use alkyd paints.

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