Shellac
Introduction
The natural resin shellac has been known in India and China for nearly 4000 years. In
Europe, shellac was introduced about 300 years ago.
Shellac is the only commercially used natural resin of animal origin and is quite
different from all other natural resins. The word shellac derived most probably from the
Indian word Laksha (one hundred thousand) and is only used for the refined or processed
resin. In its first stages the resin is known as sticklac or seedlac. Millions of tiny
parasitic insects (Kerria Lacca) produce a resinous secretion as a protective for their
larvae. The secretion forms hard layers on branches and twigs of various trees and bushes
in India and Thailand. These coated branches are cut and broken into small pieces. After
crushing the sticklac, resin and wood are separated by mechanical means. The remaining
resin is ground, washed - to partly remove the colouring agent (Lac Dye) - and finally
dried. The resulting seedlac is the raw material for all shellac production. In India,
shellac is mainly produced by the melting process, sometimes in very traditional ways
(handmade-shellac). These so called "Indian Shellacs", which all contain wax,
are available in several colour grades (Lemon, Honey, Ivory, etc.).
Besides these Indian Shellacs, there exists the "dewaxed flake shellacs".
Properties
Shellac
- is a hard, amorphous resin
- has a good resistance against solvents based on hydrocarbons
- is not toxic
- is physiologically harmless
- is thermoplastic
- is approved for various applications in the food industry
- has a low melting point (about 90°C)
- is soluble in lower alcohols and various other solvants
- is UV-resistant
- is water soluble in water-alkaline solutions
- has excellent dielectric properties, dielectric strength, a low dielectric constant,
good tracking resistance, etc.
- has excellent film forming properties
- forms smooth, high gloss films and surfaces
- coatings do not change their electrical properties under UV-radiation
- coatings have excellent adhesion to many substrates
- coatings can be polished
- has a low thermal conductivity and a low coefficient of expansion.
Applications
Shellac was used as a wood polish for music instruments and
furniture and later for uses in antifouling paints for ships, phonographic records, wood
and wallpaper paints, printing inks, resins for electrical applications, floor polishes,
etc.
Over the years the use of shellac in some of theses applications disappeared. New
applications like the coating of fruits and vegetables, food and confections, pills,
tablets, vitamins in the pharmaceutical industry are important uses for shellac today, in
addition to continued use in woodcoatings, printing inks, leather finishes, stone
polishing etc. New modified shellac resins are of great interest for waterbased coatings
and water-based printing inks.
More recently, as a new awareness about the environment and the toxicity of chemical raw
materials is noticeable everywhere, shellac or shellac modified resins are gaining
importance due to their interesting and unique characteristics. Shellacs nontoxic and
physiologically harmless characteristics as well as watersolubility, biological degration,
filmforming properties, excellent adhesion, hardness, high gloss, superior electrical
properties, compatibility with other resins, crosslinking properties, etc. allow many new
applications along with a renaissance of certain uses in industries it once dominated.
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