Q.
I have heard about lacquers that are absolutely "water white", remaining colorless even when the finish is exposed to sunlight. Names like Acrylic or CAB lacquers appear on the labels of these products. What do these names mean and what are the differences between these materials and ordinary lacquers?
A.
Conventional lacquers are formulated principally from the resin known as nitrocellulose. This is a material that is soluble in lacquer thinners, and forms a colorless solution. However, it is too hard and brittle to be a wood finish without plasticizer or modification with a less brittle resin. The choice of this modifying resin determines the color of the lacquer. Inexpensive malaic resin modified products are amber colored lacquers. More expensive coconut alkyd modification produces the so-called water white nitrocellulose lacquer, which is, in fact, also yellow, but not as amber as the malaic modified variety. Furthermore, the dry film of any nitrocellulose lacquer will yellow with age and this property is accelerated by exposure to sunlight.
With the recent and ever increasing popularity of pickle white, solid white, near white and off white wood finishes, a need has been created for truly crystal clear finishes that are also completely non-yellowing on aging. Both white lacquers and clear coats used over white lacquers must exhibit these properties, because a yellowed white finish is aesthetically unacceptable. Lacquers made only from acrylic resin are characterized by a completely crystal clear color and no discoloration or yellowing upon aging or exposure to sunlight. However, they tend to be low in solids, difficult to spray, and have poor solvent release.
CAB is an acronym for Cellulose Acetate Butyrate. Lacquers made from this very expensive resin are also completely crystal clear and non-yellowing. When blended with an acrylic resin, CAB improves solids, sprayability, flow and leveling, and solvent release. The resultant finish is also tougher and more resistant than either resin used alone.
Non-yellowing lacquers made from a complementary, cost-effective blend of CAB and acrylic resins are often called by either name, but are typically a synergistic mixture of the two. Nitrocellulose lacquer materials "fortified" with either acrylic or CAB resins must be used with caution if yellowing is a concern. They may not yellow as quickly, or as much, but they will eventually discolor.
Woodrow "Woody" Sanders is the Technical Information Director at Sampson Coatings, Inc.
